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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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50
libc/runtime/clone.c
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@ -48,6 +48,7 @@
#include "libc/sock/internal.h"
#include "libc/stdalign.internal.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/arch.h"
#include "libc/sysv/consts/clone.h"
#include "libc/sysv/consts/futex.h"
#include "libc/sysv/consts/nr.h"
@ -63,6 +64,9 @@
#define kMaxThreadIds 32768
#define kMinThreadId 262144
#define AMD64_SET_FSBASE 129
#define AMD64_SET_GSBASE 131
#define __NR_thr_new 455
#define __NR_clone_linux 56
#define __NR__lwp_create 309
@ -90,6 +94,7 @@ struct CloneArgs {
void *arg;
};
int sys_set_tls();
int __stack_call(void *, int, long, long, int (*)(void *, int), void *);
static struct CloneArgs *AllocateCloneArgs(char *stk, size_t stksz) {
@ -390,14 +395,14 @@ static int CloneNetbsd(int (*func)(void *, int), char *stk, size_t stksz,
////////////////////////////////////////////////////////////////////////////////
// FREE BESIYATA DISHMAYA
void bone(struct CloneArgs *wt) {
*wt->ztid = 0;
}
static wontreturn void FreebsdThreadMain(void *p) {
struct CloneArgs *wt = p;
#ifdef __aarch64__
asm volatile("mov\tx28,%0" : /* no outputs */ : "r"(wt->tls));
#elif defined(__x86_64__)
if (__tls_morphed) {
sys_set_tls(AMD64_SET_GSBASE, wt->tls);
}
#endif
*wt->ctid = wt->tid;
wt->func(wt->arg, wt->tid);
@ -534,6 +539,13 @@ static errno_t CloneSilicon(int (*fn)(void *, int), char *stk, size_t stksz,
////////////////////////////////////////////////////////////////////////////////
// GNU/SYSTEMD
struct LinuxCloneArgs {
int (*func)(void *, int);
void *arg;
char *tls;
int ctid;
};
int sys_clone_linux(int flags, // rdi
long sp, // rsi
int *ptid, // rdx
@ -542,24 +554,40 @@ int sys_clone_linux(int flags, // rdi
void *func, // r9
void *arg); // 8(rsp)
static int LinuxThreadEntry(void *arg, int tid) {
struct LinuxCloneArgs *wt = arg;
sys_set_tls(ARCH_SET_GS, wt->tls);
return wt->func(wt->arg, tid);
}
static int CloneLinux(int (*func)(void *arg, int rc), char *stk, size_t stksz,
int flags, void *arg, void *tls, int *ptid, int *ctid) {
int rc;
long sp;
struct LinuxCloneArgs *wt;
sp = (intptr_t)(stk + stksz);
if (~flags & CLONE_CHILD_SETTID) {
flags |= CLONE_CHILD_SETTID;
sp -= sizeof(int);
sp = sp & -alignof(int);
ctid = (int *)sp;
sp -= 8; // experiment
}
sp -= sizeof(struct LinuxCloneArgs);
// align the stack
#ifdef __aarch64__
sp = sp & -128; // for kernel 4.6 and earlier
#else
sp = sp & -16;
#endif
wt = (struct LinuxCloneArgs *)sp;
#ifdef __x86_64__
if ((flags & CLONE_SETTLS) && __tls_morphed) {
flags &= ~CLONE_SETTLS;
wt->arg = arg;
wt->tls = tls;
wt->func = func;
func = LinuxThreadEntry;
arg = wt;
}
#endif
if (~flags & CLONE_CHILD_SETTID) {
flags |= CLONE_CHILD_SETTID;
ctid = &wt->ctid;
}
if ((rc = sys_clone_linux(flags, sp, ptid, ctid, tls, func, arg)) >= 0) {
// clone() is documented as setting ptid before return
return 0;