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wasm2c: Implement PT_GNU_STACK-based stack size expansion #22237

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wasm2c: Implement PT_GNU_STACK-based stack size expansion #22237

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6578d9b
wasm2c: Implement PT_GNU_STACK-based stack size expansion.
alexrp Dec 15, 2024
7f9f91d
cmake, bootstrap.c: Set a 16 MiB stack size for zig1.
alexrp Dec 15, 2024
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10 changes: 9 additions & 1 deletion CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -805,19 +805,24 @@ if(MSVC)
set(ZIG_WASM2C_COMPILE_FLAGS "")
set(ZIG1_COMPILE_FLAGS "/Os")
set(ZIG2_COMPILE_FLAGS "/Od")
set(ZIG1_LINK_FLAGS "/STACK:16777216")
set(ZIG2_LINK_FLAGS "/STACK:16777216 /FORCE:MULTIPLE")
else()
set(ZIG_WASM2C_COMPILE_FLAGS "-std=c99 -O2")
set(ZIG1_COMPILE_FLAGS "-std=c99 -Os")
set(ZIG2_COMPILE_FLAGS "-std=c99 -O0 -fno-stack-protector")
if(APPLE)
set(ZIG1_LINK_FLAGS "-Wl,-stack_size,0x1000000")
set(ZIG2_LINK_FLAGS "-Wl,-stack_size,0x10000000")
elseif(MINGW)
set(ZIG1_LINK_FLAGS "-Wl,--stack,0x1000000")
set(ZIG2_LINK_FLAGS "-Wl,--stack,0x10000000")
# Solaris/illumos ld(1) does not provide a --stack-size option.
elseif(CMAKE_HOST_SOLARIS)
unset(ZIG1_LINK_FLAGS)
unset(ZIG2_LINK_FLAGS)
else()
set(ZIG1_LINK_FLAGS "-Wl,-z,stack-size=0x1000000")
set(ZIG2_LINK_FLAGS "-Wl,-z,stack-size=0x10000000")
endif()
endif()
Expand All @@ -839,7 +844,10 @@ add_custom_command(
)

add_executable(zig1 ${ZIG1_C_SOURCE} stage1/wasi.c)
set_target_properties(zig1 PROPERTIES COMPILE_FLAGS ${ZIG1_COMPILE_FLAGS})
set_target_properties(zig1 PROPERTIES
COMPILE_FLAGS ${ZIG1_COMPILE_FLAGS}
LINK_FLAGS "${ZIG1_LINK_FLAGS}"
)

if(MSVC)
target_link_options(zig1 PRIVATE /STACK:0x10000000)
Expand Down
9 changes: 8 additions & 1 deletion bootstrap.c
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Expand Up @@ -114,7 +114,14 @@ int main(int argc, char **argv) {
}
{
const char *child_argv[] = {
cc, "-o", "zig1", "zig1.c", "stage1/wasi.c", "-std=c99", "-Os", "-lm", NULL,
cc, "-o", "zig1", "zig1.c", "stage1/wasi.c",
"-std=c99", "-Os", "-lm",
#if defined(__APPLE__)
"-Wl,-stack_size,0x1000000",
#else
"-Wl,-z,stack-size=0x1000000",
#endif
NULL,
};
print_and_run(child_argv);
}
Expand Down
1 change: 1 addition & 0 deletions lib/std/start.zig
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Expand Up @@ -571,6 +571,7 @@ fn posixCallMainAndExit(argc_argv_ptr: [*]usize) callconv(.c) noreturn {
std.posix.exit(callMainWithArgs(argc, argv, envp));
}

// This code should be kept in sync with stage1/wasi.c.
fn expandStackSize(phdrs: []elf.Phdr) void {
for (phdrs) |*phdr| {
switch (phdr.p_type) {
Expand Down
34 changes: 34 additions & 0 deletions stage1/wasi.c
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Expand Up @@ -5,6 +5,18 @@
#include <string.h>
#include <time.h>

#if defined(__linux__)
#include <elf.h>
#include <sys/auxv.h>
#include <sys/resource.h>

#if ULONG_MAX == 0xffffffff
typedef Elf32_Phdr Elf_Phdr;
#else
typedef Elf64_Phdr Elf_Phdr;
#endif
#endif

Comment on lines +8 to +19
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this code was intentionally written to not depend on posix or os-specific things. This patch breaks that. Please stick to only the C language and standard libc in wasm2c.

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As I noted on #22111 (comment) and on Zulip, the kernel's indifference to PT_GNU_STACK leaves us with not a lot of options.

If you'd prefer, we could setrlimit(RLIMIT_STACK, ...) just before fork()ing in bootstrap.c, which already has -- and will grow more -- platform-specific code. We already hardcode the stack size values in that file anyway, so perhaps that's more fitting.

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I think that's the right way to go 👍

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Although one downside of that approach is that it won't help if you're using CMake.

Do we care? Are we getting rid of CMake once we get rid of the LLVM dependency?

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yes and it will be a glorious day

#include "panic.h"

#define LOG_TRACE 0
Expand Down Expand Up @@ -236,6 +248,28 @@ static void *dupe(const void *data, size_t len) {
}

int main(int argc, char **argv) {
// This stack size code should be kept in sync with `expandStackSize` in lib/std/start.zig.
#if defined(__linux__)
Elf_Phdr *at_phdr = (Elf_Phdr *)getauxval(AT_PHDR);
unsigned long at_phnum = getauxval(AT_PHNUM);

for (Elf_Phdr *phdr = at_phdr; phdr < at_phdr + at_phnum; phdr++) {
if (phdr->p_type != PT_GNU_STACK) continue;
if (phdr->p_memsz == 0) break;

struct rlimit limit;
if (getrlimit(RLIMIT_STACK, &limit) != 0) break;

rlim_t stack_size = phdr->p_memsz < limit.rlim_max ? phdr->p_memsz : limit.rlim_max;
if (stack_size > limit.rlim_cur) {
limit.rlim_cur = stack_size;
setrlimit(RLIMIT_STACK, &limit);
}

break;
}
#endif

if (argc < 2) {
fprintf(stderr, "usage: %s <zig-lib-path> <args...>\n", argv[0]);
return 1;
Expand Down