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Implement swapcontext() and makecontext()

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This change introduces support for Linux-style uc_context manipulation
that's fast and works well on all supported OSes and architectures. It
also integrates with the Cosmpolitan runtime which can show backtraces
comprised of multiple stacks and fibers. See the test and example code
for further details. This will be used by Mold once it's been vendored
This commit is contained in:
Justine Tunney 2023-07-02 03:50:29 -07:00
parent 7ec84655b4
commit 197aa0d465
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GPG key ID: BE714B4575D6E328
28 changed files with 617 additions and 355 deletions
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examples/setcontext.c Normal file
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#if 0
/*─────────────────────────────────────────────────────────────────╗
│ To the extent possible under law, Justine Tunney has waived │
│ all copyright and related or neighboring rights to this file, │
│ as it is written in the following disclaimers: │
│ • http://unlicense.org/ │
│ • http://creativecommons.org/publicdomain/zero/1.0/ │
╚─────────────────────────────────────────────────────────────────*/
#endif
#include "libc/calls/calls.h"
#include "libc/calls/ucontext.h"
#include "libc/runtime/runtime.h"
#include "libc/stdio/stdio.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/exit.h"
/**
* @fileoverview swapcontext() and makecontext() example
* @note adapted from the Linux man-pages project
*/
static ucontext_t uctx_main;
static ucontext_t uctx_func1;
static ucontext_t uctx_func2;
#define say(s) write(1, s, strlen(s))
#define handle_error(msg) \
do { \
perror(msg); \
exit(EXIT_FAILURE); \
} while (0)
static void func1(void) {
say("func1: started\n");
say("func1: swapcontext(&uctx_func1, &uctx_func2)\n");
if (swapcontext(&uctx_func1, &uctx_func2) == -1) {
handle_error("swapcontext");
}
say("func1: returning\n");
}
static void func2(void) {
say("func2: started\n");
say("func2: swapcontext(&uctx_func2, &uctx_func1)\n");
if (swapcontext(&uctx_func2, &uctx_func1) == -1) {
handle_error("swapcontext");
}
say("func2: returning\n");
}
int main(int argc, char *argv[]) {
char func1_stack[8192];
char func2_stack[8192];
if (getcontext(&uctx_func1) == -1) {
handle_error("getcontext");
}
uctx_func1.uc_stack.ss_sp = func1_stack;
uctx_func1.uc_stack.ss_size = sizeof(func1_stack);
uctx_func1.uc_link = &uctx_main;
makecontext(&uctx_func1, func1, 0);
if (getcontext(&uctx_func2) == -1) {
handle_error("getcontext");
}
uctx_func2.uc_stack.ss_sp = func2_stack;
uctx_func2.uc_stack.ss_size = sizeof(func2_stack);
/* Successor context is f1(), unless argc > 1 */
uctx_func2.uc_link = (argc > 1) ? NULL : &uctx_func1;
makecontext(&uctx_func2, func2, 0);
say("main: swapcontext(&uctx_main, &uctx_func2)\n");
if (swapcontext(&uctx_main, &uctx_func2) == -1) {
handle_error("swapcontext");
}
say("main: exiting\n");
exit(EXIT_SUCCESS);
}