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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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28
libc/intrin/maps.c
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@ -19,12 +19,14 @@
#include "libc/intrin/maps.h"
#include "ape/sections.internal.h"
#include "libc/calls/state.internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/cosmo.h"
#include "libc/dce.h"
#include "libc/intrin/describebacktrace.h"
#include "libc/intrin/dll.h"
#include "libc/intrin/kprintf.h"
#include "libc/intrin/maps.h"
#include "libc/macros.h"
#include "libc/nexgen32e/rdtsc.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/stack.h"
@ -72,16 +74,30 @@ void __maps_stack(char *stackaddr, int pagesz, int guardsize, size_t stacksize,
void __maps_init(void) {
int pagesz = __pagesize;
// initialize lemur64 rng
// initialize lemur64
__maps.rand = 2131259787901769494;
__maps.rand ^= rdtsc();
__maps.rand ^= kStartTsc;
// these static map objects avoid mandatory mmap() in __maps_alloc()
// they aren't actually needed for bootstrapping this memory manager
for (int i = 0; i < ARRAYLEN(__maps.spool); ++i)
__maps_free(&__maps.spool[i]);
// record _start() stack mapping
if (!IsWindows()) {
struct AddrSize stack;
stack = __get_main_stack();
__maps_stack(stack.addr, pagesz, 0, stack.size, (uintptr_t)ape_stack_prot,
0);
// linux v4.12+ reserves 1mb of guard space beneath rlimit_stack
// https://lwn.net/Articles/725832/. if we guess too small, then
// slackmap will create a bunch of zombie stacks in __print_maps
// to coverup the undisclosed memory but no cost if we guess big
size_t guardsize = (__maps.rand % 8 + 1) * 1000 * 1024;
guardsize += __pagesize - 1;
guardsize &= -__pagesize;
// track the main stack region that the os gave to start earlier
struct AddrSize stack = __get_main_stack();
__maps_stack(stack.addr - guardsize, pagesz, guardsize,
guardsize + stack.size, (uintptr_t)ape_stack_prot, 0);
}
// record .text and .data mappings