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Improve memory manager and signal handling

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On Windows, mmap() now chooses addresses transactionally. It reduces the
risk of badness when interacting with the WIN32 memory manager. We don't
throw darts anymore. There is also no more retry limit, since we recover
from mystery maps more gracefully. The subroutine for combining adjacent
maps has been rewritten for clarity. The print maps subroutine is better

This change goes to great lengths to perfect the stack overflow code. On
Windows you can now longjmp() out of a crash signal handler. Guard pages
previously weren't being restored properly by the signal handler. That's
fixed, so on Windows you can now handle a stack overflow multiple times.
Great thought has been put into selecting the perfect SIGSTKSZ constants
so you can save sigaltstack() memory. You can now use kprintf() with 512
bytes of stack available. The guard pages beneath the main stack are now
recorded in the memory manager.

This change fixes getcontext() so it works right with the %rax register.
This commit is contained in:
Justine Tunney 2024-12-27 01:03:11 -08:00
parent 36e5861b0c
commit 379cd77078
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GPG key ID: BE714B4575D6E328
48 changed files with 834 additions and 570 deletions
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9
libc/calls/sigaltstack.c
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@ -113,7 +113,7 @@ static int sigaltstack_bsd(const struct sigaltstack *neu,
* struct sigaction sa;
* struct sigaltstack ss;
* ss.ss_flags = 0;
* ss.ss_size = sysconf(_SC_MINSIGSTKSZ) + 8192;
* ss.ss_size = sysconf(_SC_SIGSTKSZ);
* ss.ss_sp = malloc(ss.ss_size);
* sigaltstack(&ss, 0);
* sigemptyset(&sa.ss_mask);
@ -121,11 +121,16 @@ static int sigaltstack_bsd(const struct sigaltstack *neu,
* sa.sa_handler = OnStackOverflow;
* sigaction(SIGSEGV, &sa, 0);
*
* Your stack size should be `sysconf(_SC_SIGSTKSZ)` which should be
* somewhere in the ballpark of 32kb to 64kb. You should go no lower
* than `sysconf(_SC_MINSIGSTKSZ) + 2048` which could be 4kb - 34kb.
* Cosmo also defines `SIGSTKSZ` as 32kb, which should also be safe.
*
* @param neu if non-null will install new signal alt stack
* @param old if non-null will receive current signal alt stack
* @return 0 on success, or -1 w/ errno
* @raise EFAULT if bad memory was supplied
* @raise ENOMEM if `neu->ss_size` is less than `MINSIGSTKSZ`
* @raise ENOMEM if `neu->ss_size` is beneath `sysconf(_SC_MINSIGSTKSZ)`
*/
int sigaltstack(const struct sigaltstack *neu, struct sigaltstack *old) {
int rc;