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Make cosmo_dlopen() safer and faster

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If cosmo_dlopen() is linked on AMD64 then the runtime will switch to
using %gs for thread-local storage. This eliminates the need for the
imported symbol trampoline. It's now safer to pass function pointers
back and forth with imported libraries. Your program gets recompiled
at runtime to make it happen and the overhead is a few milliseconds.
This commit is contained in:
Justine Tunney 2024-01-05 20:36:57 -08:00
parent c0eacf2eb1
commit fad1279c61
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GPG key ID: BE714B4575D6E328
8 changed files with 93 additions and 16 deletions
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7
libc/runtime/set_tls.c
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@ -26,6 +26,9 @@
#include "libc/thread/tls.h"
#include "libc/thread/tls2.internal.h"
#define AMD64_SET_FSBASE 129
#define AMD64_SET_GSBASE 131
int sys_set_tls();
// we can't allow --ftrace here because cosmo_dlopen() calls this
@ -37,9 +40,9 @@ dontinstrument textstartup void __set_tls(struct CosmoTib *tib) {
if (IsWindows()) {
asm("mov\t%1,%%gs:%0" : "=m"(*((long *)0x1480 + __tls_index)) : "r"(tib));
} else if (IsFreebsd()) {
sys_set_tls(129 /*AMD64_SET_FSBASE*/, tib);
sys_set_tls(__tls_morphed ? AMD64_SET_GSBASE : AMD64_SET_FSBASE, tib);
} else if (IsLinux()) {
sys_set_tls(ARCH_SET_FS, tib);
sys_set_tls(__tls_morphed ? ARCH_SET_GS : ARCH_SET_FS, tib);
} else if (IsNetbsd()) {
// netbsd has sysarch(X86_SET_FSBASE) but we can't use that because
// signal handlers will cause it to be reset due to not setting the