Understanding thread stack sizes and how Alpine is different(ariadne.space)
ariadne.space
Understanding thread stack sizes and how Alpine is different
https://ariadne.space/2021/06/25/understanding-thread-stack-sizes-and-how-alpine-is-different/
80 comments
> The wording sounds as if it is trying to assign blame for the problem.
Yes. It sound like someone that have been in a million discussion about why "that your program crashes is not a bug in our operating system".
Many people, even engineers, expect things to behave as they usually do instead of behave as specified. So, I can imagine how all that discussions go.
Yes. It sound like someone that have been in a million discussion about why "that your program crashes is not a bug in our operating system".
Many people, even engineers, expect things to behave as they usually do instead of behave as specified. So, I can imagine how all that discussions go.
> What, then, is the guaranteed thread stack size?
If you need a big stack, you can just ask pthread to give you one.
If you need a big stack, you can just ask pthread to give you one.
> The wording sounds as if it is trying to assign blame for the problem.
Yes. Sadly, people often write incorrect programs.
> What, then, is the guaranteed thread stack size?
I can't be bothered to look up the POSIX guarantees, the gist of it anyway is that it depends on the application developer and system administrator.
> A developer would obviously need to know this (and other things such as the amount of stack size required by variables, parameters and frames) to not fall into this trap of writing non-portable programs.
If you're not going to calculate the exact requirements (probably unnecessary), guess/measure a number of bytes and allocate a stack that's 50 or 100 times greater than that. That's better than ignoring the existence of the stack, anyway.
Yes. Sadly, people often write incorrect programs.
> What, then, is the guaranteed thread stack size?
I can't be bothered to look up the POSIX guarantees, the gist of it anyway is that it depends on the application developer and system administrator.
> A developer would obviously need to know this (and other things such as the amount of stack size required by variables, parameters and frames) to not fall into this trap of writing non-portable programs.
If you're not going to calculate the exact requirements (probably unnecessary), guess/measure a number of bytes and allocate a stack that's 50 or 100 times greater than that. That's better than ignoring the existence of the stack, anyway.
Why would you overcomplicate your life and use something like the autofree example, that is not even portable, if you can use the heap which is simple to understand and do? I understand that if it is a hot function you may run into memory fragmentation/performance issues, but there are some many ways to deal with that with custom allocators if it truly is a problem. This is one of those perfect examples where simple is better IMHO
The autofree example uses the heap. It just makes calling free() automatic when the function returns, regardless of where it does so. It's leak protection.
It's also wrong since __attribute__((cleanup)) expects a function that takes an additional level of pointer. In this case, it'll call "free(&scratchpad);". Which doesn't get you a compiler warning in C because passing a char ** as a void * is perfectly fine. But your heap is f*cked after this.
Correct way to do it is
It's also wrong since __attribute__((cleanup)) expects a function that takes an additional level of pointer. In this case, it'll call "free(&scratchpad);". Which doesn't get you a compiler warning in C because passing a char ** as a void * is perfectly fine. But your heap is f*cked after this.
Correct way to do it is
void free2(char **p)
{
free(*p);
}
#define autofree __attribute__((cleanup(free2)))The proposed autofree example uses the heap with (unnecessary) preprocesor directives... but the problem is that it is not portable as written, vs simply using the heap like a normal person.
Makes you wonder what else they can tweak that would be correct according to one spec or another but would still trip up people who assumed reasonable defaults, and why they don't do that as well.
In other words, use heap space and not stack space. This is pretty elementary in C programming.
That might have been true in the old days when memory wasn't the bottleneck, but in today's world where a cache miss is catastrophic, it makes MUCH more sense to use stack space where you can. This also has the side effect of facilitating idempotent functions and function purity in general.
No sense in clinging to old world ideals when they no longer make sense.
No sense in clinging to old world ideals when they no longer make sense.
That is certainly a take.
Storing small data, like function-local ints, pointers, etc, on the stack is beneficial due to L1$ prefetching semantics, but storing a 512KB scratchpad on the stack (which is what the article is about) will totally trash your L1$ and you'll have MORE cache misses than you would if that scratchpad was not on the stack.
Storing small data, like function-local ints, pointers, etc, on the stack is beneficial due to L1$ prefetching semantics, but storing a 512KB scratchpad on the stack (which is what the article is about) will totally trash your L1$ and you'll have MORE cache misses than you would if that scratchpad was not on the stack.
I agree that using the stack instead of heap makes sense for cache reasons.
But in the contemporary world, the trend is increasingly to transform functions to "async" forms where much of the functions' local state including return address is stored in heap-allocated space instead.
But in the contemporary world, the trend is increasingly to transform functions to "async" forms where much of the functions' local state including return address is stored in heap-allocated space instead.
this is too reductive. Usually stack space is faster because you will have fewer cache misses.
future languages will be able to suss this out at compile-time: https://github.com/ziglang/zig/blob/2ac769eab9b7dba4cd38e5de...
future languages will be able to suss this out at compile-time: https://github.com/ziglang/zig/blob/2ac769eab9b7dba4cd38e5de...
If speed issues then it sounds like this is critical code path that is sensitive to time. You'd be looking for alternative data structures at that point so this point would be moot.
It's a bit ridiculous to complicate recursive algorithms just because the stack sizes haven't been increased in the past 3 decades.
Nowadays we have at least 48bit virtual address space available; what's the harm in giving each thread a full GB of stack?
Nowadays we have at least 48bit virtual address space available; what's the harm in giving each thread a full GB of stack?
Sure, but 128 kB is really small even if you do that properly.
Seems like it would be more sensible if the stack space could just grow when required. Surely not that difficult?
Seems like it would be more sensible if the stack space could just grow when required. Surely not that difficult?
Since standard OS stacks are contiguous and unmovable, you can't grow them once they run out of space. However while the address space for the maximum stack size gets reserved, each page only requires backing memory once it's first used. So as far as physical memory consumption is concerned, typical stacks act as growable with a fixed maximum size. Since address space is huge on 64-bit systems, choosing a large stack size is cheap on such systems (at least of they allow over-commit).
For the main thread, a system can also try to keep other allocations far from the stack without committing to any particular size (heap grows upwards from the bottom of the address space, stack downwards from the top). But this doesn't scale to multiple threads and leads to an unpredictable maximum stack size, so I prefer the fixed reserved space approach.
For the main thread, a system can also try to keep other allocations far from the stack without committing to any particular size (heap grows upwards from the bottom of the address space, stack downwards from the top). But this doesn't scale to multiple threads and leads to an unpredictable maximum stack size, so I prefer the fixed reserved space approach.
The main thread already does that. The thread stack does not. It probably made sense on 32b with relatively limited address space... But I'm curious why we're not applying that to all threads on 64b. Reserving a few 10MB of address space per thread shouldn't be a big issue, right? (Without actually mapping those pages)
Mapping a lot of pages has some overhead, too. So if you have large stacks per thread you'll take a hit.
If you use huge pages to alleviate that, you'll waste a lot of physical memory.
If you use huge pages to alleviate that, you'll waste a lot of physical memory.
It is easy for a single threaded program, but since each thread has it's own part of the stack, it would be non-trivial for a multithreaded program.
Wait until you realize OS kernel thread stack size is 8 KiB or in that range, if you think 128 KiB is small. :))
Enough for a full COM binary plus one overlay section. :)
A typical stack frame is around a couple dozen words. Let's round that up to 32 words (256 bytes). 128K is enough for a 500 deep stack at that size. 128K is huge.
I'd say "be aware of stack sizes". If you can get away with just the appropriately sized stack in a thread, that's a nice performance gain over dealing with multithreading heap allocators.
How can you write a program that runs without at least some guaranteed stack size? Are you at fault if you program doesn't run in a 1kb stack? And how do you work out what stack size your program takes from looking at the source code?
I guess make sure your required stack size is not a function of input, and test against a minimum stack size.
I guess make sure your required stack size is not a function of input, and test against a minimum stack size.
GCC has “-fstack-usage”
In general, you just can't. This means that any function call in C can bust the stack, unfortunately. You can try to use heuristics to try to avoid using up large amounts of space (avoid alloca and large stack arrays, be careful about recursion) but other than that there isn't much you can do.
Unless you do alloca() or dynamically sized local arrays, you can measure your stack usage in the deepest call stack. Add some space in each frame for potential instrumentation and you have your minimum.
Keep in mind that this is just for thread stacks - you can set the size for them yourself, so ideally you'd always do it. Then a guaranteed minimum size becomes irrelevant.
Keep in mind that this is just for thread stacks - you can set the size for them yourself, so ideally you'd always do it. Then a guaranteed minimum size becomes irrelevant.
> Unless you do alloca() or dynamically sized local arrays, you can measure your stack usage in the deepest call stack.
How does a normal working programmer calculate the size of each of their stack frames? I'm a compiler researcher and I'd struggle to do that. How are application developers going to do it?
And how do you design a program to have a deterministic maximum call stack depth?
I don't think these things are as easy as you're making out.
How does a normal working programmer calculate the size of each of their stack frames? I'm a compiler researcher and I'd struggle to do that. How are application developers going to do it?
And how do you design a program to have a deterministic maximum call stack depth?
I don't think these things are as easy as you're making out.
If we forbid things like recursion (including mutual recursion), function pointers, dynamic dispatch, and unbounded use of alloca, doesn't it then follow from the call graph and the per-function worst-case stack-usage numbers (which the compiler presumably knows)? Is that mistaken, or is the difficulty in generalising this approach to where those restrictions are lifted?
I tried googling for how SPARK Ada provides assurances against exceeding stack-size limits, but I couldn't find a decent answer. I presume it does so, though.
edit: forgot about alloca
edit 2: Turns out the AdaCore folks have a tool specifically for static analysis of stack-space requirements of Ada/C/C++ code: https://www.adacore.com/gnatpro/toolsuite/gnatstack
I tried googling for how SPARK Ada provides assurances against exceeding stack-size limits, but I couldn't find a decent answer. I presume it does so, though.
edit: forgot about alloca
edit 2: Turns out the AdaCore folks have a tool specifically for static analysis of stack-space requirements of Ada/C/C++ code: https://www.adacore.com/gnatpro/toolsuite/gnatstack
You have 2 options: either your functions are recursive and you can hope and pray, or they're not and you can figure out which of your functions are the bottom of the call graph.
In those leaf functions you can check &local_var and compare it to pthread_attr_getstack(pthread_getattr_np()). (Of course that's not precise for many reasons.)
> And how do you design a program to have a deterministic maximum call stack depth?
If you're running only your code - don't use recursion, or alloca. If you use external libraries, you have to research what they do and add some extra in case of updates.
Bounded stack size is also a common issue if you're targeting small microprocessors.
For non-critical apps it should be pretty easy to figure out the needed stack size. For cases when you want to guarantee it... that gets more tricky.
Edit: just learned that clang has the option -fstack-usage which should help a lot.
In those leaf functions you can check &local_var and compare it to pthread_attr_getstack(pthread_getattr_np()). (Of course that's not precise for many reasons.)
> And how do you design a program to have a deterministic maximum call stack depth?
If you're running only your code - don't use recursion, or alloca. If you use external libraries, you have to research what they do and add some extra in case of updates.
Bounded stack size is also a common issue if you're targeting small microprocessors.
For non-critical apps it should be pretty easy to figure out the needed stack size. For cases when you want to guarantee it... that gets more tricky.
Edit: just learned that clang has the option -fstack-usage which should help a lot.
Dynamic dispatch (e.g. function pointers/delegates, virtual methods) is another case that makes figuring out the call graph and thus the maximum stack size difficult (via whole-program data-flow analysis) to impossible (function pointers come from outside your codebase or are constructed in ways analysis can't handle).
> You have 2 options: either your functions are recursive and you can hope and pray
Or you can try to figure out the maximum number of times it'll recurse: for example, the height of a red-black tree with less than 2^64 nodes is less than 128, iirc.
Or you can try to figure out the maximum number of times it'll recurse: for example, the height of a red-black tree with less than 2^64 nodes is less than 128, iirc.
One rather quickly runs into halting-problem type issues, especially in the function dispatch method. Imagine a DSL that does stuff, and is implemented by function pointers in the parser/interpreter, and then the question becomes one of program inputs. In any case, having such a small limit is crazy, and defending it with references to correctness smells of Ulrich Drepper and the memmove issue. The whole "sucks less" movement is a little too focused on purity for my taste. The only time I'm sad when I look at my memory usage on my personal laptop is when I have unused memory. Please, pre-fetch some news.ycombinator, cache some more inodes for my next ncdu or find command; I have already paid for the memory, not using it is silly. Sure, we software engineers get lazy, but, except in AWS, use all your memory, all your processors upto throttling, all the time. Why not?
I remember one day in the 90s counting out like max address len and max zip code len and so and trying to figure out how long to make my target stack allocated buffer, and i was like fuck it, I have more important things to do, all my stack buffers are hence forth 65536 bytes long.
I remember one day in the 90s counting out like max address len and max zip code len and so and trying to figure out how long to make my target stack allocated buffer, and i was like fuck it, I have more important things to do, all my stack buffers are hence forth 65536 bytes long.
Not easy at all.
I know that in the small-embedded world, people do work on such things.
Eg https://github.com/japaric/cargo-call-stack
I know that in the small-embedded world, people do work on such things.
Eg https://github.com/japaric/cargo-call-stack
You ask a compiler, since it knows the max stack requirements of every function it compiled, if it's fixed. If it's not fixed it may give you at least the minimum.
For total depth, keeping you program simple and predictable helps. People certainly manage to do it even for large programs like Linux itself, where stack size is like 16KiB or so. https://elixir.bootlin.com/linux/v5.2/source/arch/x86/includ... and less on other archs. 8 KiB on arm https://elixir.bootlin.com/linux/v5.13-rc7/source/arch/arm/i...
For total depth, keeping you program simple and predictable helps. People certainly manage to do it even for large programs like Linux itself, where stack size is like 16KiB or so. https://elixir.bootlin.com/linux/v5.2/source/arch/x86/includ... and less on other archs. 8 KiB on arm https://elixir.bootlin.com/linux/v5.13-rc7/source/arch/arm/i...
But the compiler may not compile simple 'functions' as the user understands them - it may compile loop bodies, functions with other functions compiled in them, individual branches of functions, multiple versions of functions based on where they're called from...
If I tell you as a compiler writer that this loop body from this function, but with this branch and this branch outlined, but only when called from this context, takes n bytes... I don't get what most working programmers are going to usefully do with that information.
If I tell you as a compiler writer that this loop body from this function, but with this branch and this branch outlined, but only when called from this context, takes n bytes... I don't get what most working programmers are going to usefully do with that information.
Where's the problem? Compiler will tell you what amount of stack a function will use, if it's inlined it may not tell you for that function, but it will tell you for the function the function was inlined to, which is what matters.
If the language is complicated and has generics or whatever, the programmer will have to do more work to understand it.
It's not a huge issue in C.
If the language is complicated and has generics or whatever, the programmer will have to do more work to understand it.
It's not a huge issue in C.
> Compiler will tell you what amount of stack a function will use
If you ask a compiler how much stack a function will use the answer for a non-trivial compiler for a complicated language is always going to be 'it depends...'
If you ask a compiler how much stack a function will use the answer for a non-trivial compiler for a complicated language is always going to be 'it depends...'
As I mentioned in my other comment, AdaCore's GNATstack tool appears to be capable of reporting this information conservatively but with enough accuracy to be useful.
https://www.adacore.com/gnatpro/toolsuite/gnatstack
https://www.adacore.com/gnatpro/toolsuite/gnatstack
The tool will simply freak out when there is any recursion or indirect call. It's not helpful since it happens everywhere in standard libraries and non trivial programs (forget about sorting, any regex, parsing source code, linting, etc...).
The only use case is for real-time embedded code -typically in aerospace- where the coding guidelines prohibits you from using any recursion at all and you have to prove the highest stack usage fits into the chosen microcontroller.
The only use case is for real-time embedded code -typically in aerospace- where the coding guidelines prohibits you from using any recursion at all and you have to prove the highest stack usage fits into the chosen microcontroller.
I mentioned such restrictions in my other comment, [0] I should have mentioned them here too.
[0] https://news.ycombinator.com/item?id=27642406
[0] https://news.ycombinator.com/item?id=27642406
Original article is about C compiled programs, not about arbitrary languages. It's not a huge problem in C.
> Add some space in each frame for potential instrumentation and you have your minimum.
On exit just scan from the maximum stack to minimum looking for non-zero.
If you have tests it should be easy to get within a few bytes of max stack used, which is probably just as good as instrumenting everything.
On exit just scan from the maximum stack to minimum looking for non-zero.
If you have tests it should be easy to get within a few bytes of max stack used, which is probably just as good as instrumenting everything.
It's possible, but you need to watch out for some cases. For example let's say your furthest function declares char foo[4096], but uses only a few bytes of it in your testing. Your measurement will be 4k short.
It has to be a leaf function or there would be stack frames after, and no local variables after the array, and the function doesn't push anything onto the stack, and it has to be possible in ways not covered by tests to actually use that space.
Sure, that could happen.
But what the other guy was saying about being a compiler developer and being unsure how to calculate the maximum depth is that there are many, many ways to arrive at the wrong result. Resursion, argv/envp, varags, alloca, and so on. So unless you are going to spend a great deal of energy proving maximum depth you're going to be using an estimate of some sort. Thus, 'probably just as good'.
Sure, that could happen.
But what the other guy was saying about being a compiler developer and being unsure how to calculate the maximum depth is that there are many, many ways to arrive at the wrong result. Resursion, argv/envp, varags, alloca, and so on. So unless you are going to spend a great deal of energy proving maximum depth you're going to be using an estimate of some sort. Thus, 'probably just as good'.
If you have to work in an environment where stack size is very limited (typically a few KiB) you have to pay attention to certain things that you can brush away in more generous environment. In particular you need to be very careful with recursive functions and you probably want to use the heap or static storage for any object bigger than a couple dozens bytes.
But in my experience you don't really compute a "guaranteed" stack size, you use your experience and knowledge of the program to make an educated guess, and then you apply a reasonable multiplier to give you some security margin.
If you don't use (or severely limit) recursive calls you can usually just check that your deepest call stack fits within the bounds. Although finding the deepest call stack in the first place can be tricky given that compilers can aggressively inline function calls.
But in my experience you don't really compute a "guaranteed" stack size, you use your experience and knowledge of the program to make an educated guess, and then you apply a reasonable multiplier to give you some security margin.
If you don't use (or severely limit) recursive calls you can usually just check that your deepest call stack fits within the bounds. Although finding the deepest call stack in the first place can be tricky given that compilers can aggressively inline function calls.
I remember reading about arguments over whether Algol should permit recursive procedures, where one side of the argument was apparently claiming that they wouldn't be possible to implement.
That seems pretty strange to modern ears, but maybe the underlying point was that it isn't possible to statically know how much stack size would be required.
I suppose it wouldn't have been obvious then that if you fudge the issue for the first thirty years or so, everyone will just accept that this is the way the world is.
Still, it's a bit of a shame that there are still widely-used systems where if you exceed the available stack space you're likely to face a "weird crash" rather than a clean error message at runtime.
That seems pretty strange to modern ears, but maybe the underlying point was that it isn't possible to statically know how much stack size would be required.
I suppose it wouldn't have been obvious then that if you fudge the issue for the first thirty years or so, everyone will just accept that this is the way the world is.
Still, it's a bit of a shame that there are still widely-used systems where if you exceed the available stack space you're likely to face a "weird crash" rather than a clean error message at runtime.
Contemporary books (incl. TAoCP Vol. 1 IIRC) don’t place return addresses on a stack or in a register at all: you’re generally told to modify the operand of the jump instruction at the end of the procedure you want to call then jump to its entry point. It took a while before reentrancy was even recognized as a possibility, let alone used (by humans or compilers) by default.
I remember reading that the call stack was invented as an implementation device for recursion as introduced in Algol, but I can’t recall how that claim was sourced.
I remember reading that the call stack was invented as an implementation device for recursion as introduced in Algol, but I can’t recall how that claim was sourced.
"but maybe the underlying point was that it isn't possible to statically know how much stack size would be required."
Given the time frame you're talking about, remember to be thinking in terms of kilobytes, not gigabytes. And potentially low-single-digit numbers of kilobytes. It could be in the range of hundreds of bytes dedicated to stacks at the time. Even if you could compute your maximum size it's easy to imagine people balking a the results of such a computation and think it's not worth it to even consider the possibility because you'd blow your stack so quickly it's not like there'd be any benefit to it.
Given the time frame you're talking about, remember to be thinking in terms of kilobytes, not gigabytes. And potentially low-single-digit numbers of kilobytes. It could be in the range of hundreds of bytes dedicated to stacks at the time. Even if you could compute your maximum size it's easy to imagine people balking a the results of such a computation and think it's not worth it to even consider the possibility because you'd blow your stack so quickly it's not like there'd be any benefit to it.
> it isn't possible to statically know how much stack size would be required.
It's not just that - if it were merely that you couldn't know the size statically, you could use dynamic memory allocation. The problem with that though, is that now every (not provably nonrecursive) function call can now fail with a memory allocation error, and if your language doesn't surface that to the caller, and (correctly) doesn't allow spurious errors to appear out of nowhere (cough every modern programming language cough cough), there's no way to handle that error.
It's not just that - if it were merely that you couldn't know the size statically, you could use dynamic memory allocation. The problem with that though, is that now every (not provably nonrecursive) function call can now fail with a memory allocation error, and if your language doesn't surface that to the caller, and (correctly) doesn't allow spurious errors to appear out of nowhere (cough every modern programming language cough cough), there's no way to handle that error.
Another complication is that in glibc's implementation TLS variables come out of the same space as the per-thread stack.
As far as I can tell this is something they think in principle should be changed.
https://sourceware.org/bugzilla/show_bug.cgi?id=11787
As far as I can tell this is something they think in principle should be changed.
https://sourceware.org/bugzilla/show_bug.cgi?id=11787
This is one of the reasons why I'm no longer using Alpine as a base in Docker images. I ran into this limit specifically with node-sass.
But in general, the difference in image size is negligible because of shared layers, and I just don't think enough testing happens on Alpine / musl in any given stack. Even if your app runtime is tested this way, how many dependencies are?
Come to think of it, I'm not even sure why there was a push for Alpine-based Docker images at some point. Maybe it was just hype.
But in general, the difference in image size is negligible because of shared layers, and I just don't think enough testing happens on Alpine / musl in any given stack. Even if your app runtime is tested this way, how many dependencies are?
Come to think of it, I'm not even sure why there was a push for Alpine-based Docker images at some point. Maybe it was just hype.
At $WORK, there's a process for automatically scanning docker images for packages that have CVEs against them. Any docker image that includes glibc instantly shoots to the top of the charts, mostly because of a boatload of high or critical severity CVEs relating to bugs in asm-implemented functions on platforms like ARM, POWER9, etc. Everything in our company runs on x86, but the CVE scanning tool is dumb, so a switch to alpine was heavily encouraged.
This broke teams that rely on python and on node, but the docker image guidelines come from a team whose ideal language is now go (and most of whose legacy code is in java), so they are not really sensitive to those concerns. Ironically we tried to move to distroless as implemented by google[1], but that's based on debian which includes glibc, so the un-nuanced CVE checker freaks out again. That effort was quietly dropped.
(I'm not actually disputing the proposition that alpine is better for security under certain circumstances, but I think a lot of "the push" comes from what might uncharitably be described as cargo culting, or with more insight as interpretations that make sense in one context [everything is a static binary, little to no reliance on traditional userland tools] being unquestioningly extended to other contexts.)
[1] https://github.com/GoogleContainerTools/distroless
This broke teams that rely on python and on node, but the docker image guidelines come from a team whose ideal language is now go (and most of whose legacy code is in java), so they are not really sensitive to those concerns. Ironically we tried to move to distroless as implemented by google[1], but that's based on debian which includes glibc, so the un-nuanced CVE checker freaks out again. That effort was quietly dropped.
(I'm not actually disputing the proposition that alpine is better for security under certain circumstances, but I think a lot of "the push" comes from what might uncharitably be described as cargo culting, or with more insight as interpretations that make sense in one context [everything is a static binary, little to no reliance on traditional userland tools] being unquestioningly extended to other contexts.)
[1] https://github.com/GoogleContainerTools/distroless
>
Come to think of it, I'm not even sure why there was a push for Alpine-based Docker images at some point.
The continuing push is due to the smaller footprint and better security properties. And no amount of sharing makes up for the difference between a single-MB image and a GB image.
Any application can just dictate its own thread stack size. What is discussed here is a default.
The continuing push is due to the smaller footprint and better security properties. And no amount of sharing makes up for the difference between a single-MB image and a GB image.
Any application can just dictate its own thread stack size. What is discussed here is a default.
A slimmer image is better from an attack surface point of view. “Distroless” with its tree shaking takes this to its logical conclusion but when images on alpine started getting popular that wasn’t available (at least to the general public).
It took some time before Ubuntu and Debian offered official slim containers... Before that, many programs in containers defaulted to Ubuntu or Debian, and it was 600MB to run something like Nginx or Apache, while alpine was 40MB
I think allocating something very large on stack should have been reviewed by peers to either fix it to use heap.
Stop being cringe and adopt the same stack size as everyone else. Oh my god. What on earth are you saving?
IMO: it's nice to have weird platforms. I've caught lurking UDB and memory corruption in my programs by trying to run them on weird OSes.
There is no UDB or memory corruption exceeding the stack size. It means your platform is too small to run the program. Of course, Alpine doesn't run on platforms that are too small, they just make nonsensical changes like these that cause incompatibilities but have zero benefits.
https://github.com/yaegashi/muslstack seems to indicate the limit is coming from musl (the libc) rather than Alpine, which may legitimately have a hope of running on small platforms.
Alpine runs on all sorts of small platforms. It is possible to run it on OpenWRT type devices.
Yeah, it sucks that programs crash on your system, but this is the way of things: The popular systems get targeted and tested in-depth, the less popular systems not so much. This is NOT the developer's fault; this is pragmatism.
And so the mountain must come to Mohamed. Increase Alpine's default stack size to something more in-line with the big boys.
And so the mountain must come to Mohamed. Increase Alpine's default stack size to something more in-line with the big boys.
No, they should keep their low stack size to the benefit of everyone.
Diversity helps discover what is fundamentally a broken and fragile assumption that a dynamic property will always have some value. An assumption that can fail anywhere, including on the OS that was initially targeted, and will fail the moment another OS is targeted.
The developer should fix their broken assumption, but is entirely free to do so by taking control of the value at link time.
Diversity helps discover what is fundamentally a broken and fragile assumption that a dynamic property will always have some value. An assumption that can fail anywhere, including on the OS that was initially targeted, and will fail the moment another OS is targeted.
The developer should fix their broken assumption, but is entirely free to do so by taking control of the value at link time.
I absolutely agree with your point about diversity. But us advocates need to understand this "pragmatic" view and counter it properly. Normally, the argument that works is: "Do you monitor the thread stack size on $POPULAR_PLATFORM so if that changes, you won't be bitte ?
I would at least make it equal to MacOS, another very popular target where things are tested a lot. That’s 512KiB. 128 is teeny.
Windows is also popular. Maybe change the process and thread stack sizes to 1MiB each? That's probably just as bad of a solution though, IMO. This article shows that assumptions are being taken for granted; no developer should expect two libc implementations to behave identically. Packagers for distros should be aware of this, too.
I'm annoyed by the fact that I have to visit "new" reddit to be able to accept cookies, and then go back to the old design. This is on desktop btw.
Wrong thread. You probably want https://news.ycombinator.com/item?id=27641366.
> As most threads only need a small amount of stack memory, other platforms use smaller limits, such as OpenBSD using only 64 KiB and Alpine using at most 128 KiB by default.
By your own table, OpenBSD uses 512 KiB unless you're on an ancient version. Among the listed, Alpine is the lone outlier.
By your own table, OpenBSD uses 512 KiB unless you're on an ancient version. Among the listed, Alpine is the lone outlier.
It woupd be nice if the article explained why was the current size set and what is the benefit of doing so?
The distinction that's being characterized as "GNU/Linux" vs. just "Alpine" is confusing.
Is Alpine using some new kernel? No, it's a Linux distribution that uses the Linux kernel, albeit with some unusual defaults.
Does Alpine not have any of the GNU userspace tools? Also no, there are plenty in the Alpine package repository.
Look, I get that GNU/Linux and ”GnU pLuS LiNuX" is a loaded term and has a lot of baggage, and that everyone would like to just be rid of the whole mess, but the characterization used here had me thinking that there was some other "Alpine kernel" experimental OS project that I had missed that had nothing to do with Alpine Linux.
The word "Linux" never once follows the word "Alpine" in this article, and it discusses overcommit mode as if it's a uniquely "GNU/Linux" thing. WTF does kernel overcommit have to do with GNU?
Please just call it what it is.
Is Alpine using some new kernel? No, it's a Linux distribution that uses the Linux kernel, albeit with some unusual defaults.
Does Alpine not have any of the GNU userspace tools? Also no, there are plenty in the Alpine package repository.
Look, I get that GNU/Linux and ”GnU pLuS LiNuX" is a loaded term and has a lot of baggage, and that everyone would like to just be rid of the whole mess, but the characterization used here had me thinking that there was some other "Alpine kernel" experimental OS project that I had missed that had nothing to do with Alpine Linux.
The word "Linux" never once follows the word "Alpine" in this article, and it discusses overcommit mode as if it's a uniquely "GNU/Linux" thing. WTF does kernel overcommit have to do with GNU?
Please just call it what it is.
So in your view, having even a single GNU tool installed, or even available for installation, means you're using "GNU/Linux"? Alpine uses musl and busybox rather than the more common GNU equivalents.
Kernel overcommit has nothing to do with GNU, but default stack size has a lot to do with which libc you use. Musl has a different default than glibc. Overcommit is mentioned because it is the justification for glibc having a large stack size by default. Musl has defaults that make fewer assumptions about how the system is configured.
Kernel overcommit has nothing to do with GNU, but default stack size has a lot to do with which libc you use. Musl has a different default than glibc. Overcommit is mentioned because it is the justification for glibc having a large stack size by default. Musl has defaults that make fewer assumptions about how the system is configured.
Okay, that's fair. I was confused and responded in frustration. Maybe glibc vs. musl would have been more clear than "GNU/Linux" vs. "Alpine".
I still think only referring to it as "Alpine" and not once calling it "Alpine Linux" is weird.
I still think only referring to it as "Alpine" and not once calling it "Alpine Linux" is weird.
> Thread-local variables are referenced with the thread_local keyword. You must include threads.h in order to use it:
[——— also, copied from a reply I posted below: ———]
The autofree macro is wrong since __attribute__((cleanup)) expects a function that takes an additional level of pointer. In this case, it'll call "free(&scratchpad);". Which doesn't get you a compiler warning in C because passing a char ** as a void * is perfectly fine. But your heap is f*cked after this.
Correct way to do it is
#include <threads.h>
void some_function(void) {
thread_local char scratchpad[500000];
memset(scratchpad, 'A', sizeof scratchpad);
}
[——— also, copied from a reply I posted below: ———]
The autofree macro is wrong since __attribute__((cleanup)) expects a function that takes an additional level of pointer. In this case, it'll call "free(&scratchpad);". Which doesn't get you a compiler warning in C because passing a char ** as a void * is perfectly fine. But your heap is f*cked after this.
Correct way to do it is
void free2(char **p)
{
free(*p);
}
#define autofree __attribute__((cleanup(free2)))
The wording sounds as if it is trying to assign blame for the problem. What, then, is the guaranteed thread stack size? A developer would obviously need to know this (and other things such as the amount of stack size required by variables, parameters and frames) to not fall into this trap of writing non-portable programs.