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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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17
libc/dlopen/dlopen.c
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@ -45,6 +45,7 @@
#include "libc/nt/memory.h"
#include "libc/nt/runtime.h"
#include "libc/proc/posix_spawn.h"
#include "libc/runtime/internal.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/syslib.internal.h"
#include "libc/serialize.h"
@ -494,6 +495,8 @@ static uint8_t *movimm(uint8_t p[static 16], int reg, uint64_t val) {
static void *foreign_thunk_sysv(void *func) {
uint8_t *code, *p;
#ifdef __x86_64__
// it is no longer needed
if (1) return func;
// movabs $func,%rax
// movabs $foreign_tramp,%r10
// jmp *%r10
@ -896,3 +899,17 @@ char *cosmo_dlerror(void) {
STRACE("dlerror() → %#s", res);
return res;
}
#ifdef __x86_64__
static textstartup void dlopen_init() {
if (IsLinux() || IsFreebsd()) {
// switch from %fs to %gs for tls
struct CosmoTib *tib = __get_tls();
__morph_tls();
__set_tls(tib);
}
}
const void *const dlopen_ctor[] initarray = {
dlopen_init,
};
#endif