Date: Mon, 08 Feb 2021 06:42:37 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 253337] Linuxulator: glibc's pthread_getattr_np reports stack size as 124K Message-ID: <bug-253337-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D253337 Bug ID: 253337 Summary: Linuxulator: glibc's pthread_getattr_np reports stack size as 124K Product: Base System Version: Unspecified Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: iwtcex@gmail.com I think it should return a value equal or slightly smaller than RLIMIT_STACK instead. It does so on Ubuntu at least. Apparently, Mono (most notably used in the popular Unity game engine) relies on this for setting stack guards: https://github.com/mono/mono/blob/da11592cbea4269971f4b1f9624769a85cc10660/= mono/utils/mono-threads-linux.c#L13-L38, https://github.com/mono/mono/blob/43190aeb5f7e4d7e0185d3b656054bf232219fe2/= mono/mini/mini-exceptions.c#L3160-L3175. Reproducer: % uname -a FreeBSD desktop 12.2-RELEASE-p1 FreeBSD 12.2-RELEASE-p1 GENERIC amd64 % cat apparent_stack_size.c #define _GNU_SOURCE #include <assert.h> #include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <unistd.h> int main() { char cmd[100]; snprintf(cmd, sizeof(cmd), "cat /proc/%d/maps | tail -n 5", getpid()); system(cmd); size_t size =3D 0; void* addr =3D NULL; pthread_attr_t attr; assert(pthread_attr_init(&attr) =3D=3D 0); assert(pthread_getattr_np(pthread_self(), &attr) =3D=3D 0); assert(pthread_attr_getstack(&attr, &addr, &size) =3D=3D 0); assert(pthread_attr_destroy(&attr) =3D=3D 0); fprintf(stderr, "stack size =3D %zd\n", size); return 0; } % /compat/linux/bin/cc apparent_stack_size.c -pthread -o test % ./test 00000008011c7000-00000008011c9000 rw-p 0038a000 00:00 391497=20=20=20=20 /compat/linux/usr/lib64/libc-2.17.so 00000008011c9000-00000008011ce000 rw-p 00000000 00:00 0 00007fffdffff000-00007ffffffdf000 ---p 00000000 00:00 0 00007ffffffdf000-00007ffffffff000 rw-p 00000000 00:00 0 [stack] 00007ffffffff000-0000800000000000 r-xs 00000000 00:00 0 [vdso] stack size =3D 126976 As it happens, glibc reads /proc/self/maps and compares the stack entry to the preceding entry. You know, just in case: /* The limit might be too high. */ if ((size_t) iattr->stacksize > (size_t) iattr->stackaddr - last_to) iattr->stacksize =3D (size_t) iattr->stackaddr - last_to; (https://sourceware.org/git/?p=3Dglibc.git;a=3Dblob;f=3Dnptl/pthread_getatt= r_np.c;h=3D25807cb529880d67a6561b6ebcd45042e89dea3e;hb=3DHEAD#l144) --=20 You are receiving this mail because: You are the assignee for the bug.=
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