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[Backtracing][Linux] Fix crash handler for musl. #82624

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Merged
merged 1 commit into from
Jul 1, 2025
Merged

[Backtracing][Linux] Fix crash handler for musl. #82624

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16 changes: 14 additions & 2 deletions stdlib/public/RuntimeModule/Elf.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -1064,8 +1064,8 @@ struct ElfSymbolTable<SomeElfTraits: ElfTraits>: ElfSymbolTableProtocol {
continue
}

// Ignore anything undefined
if symbol.st_shndx == SHN_UNDEF {
// Ignore anything undefined or absolute
if symbol.st_shndx == SHN_UNDEF || symbol.st_shndx == SHN_ABS {
continue
}

Expand Down Expand Up @@ -1190,6 +1190,8 @@ final class ElfImage<SomeElfTraits: ElfTraits>
var sectionHeaders: [Traits.Shdr]?
var shouldByteSwap: Bool { return header.shouldByteSwap }

var imageBase: ImageSource.Address

@_specialize(kind: full, where SomeElfTraits == Elf32Traits)
@_specialize(kind: full, where SomeElfTraits == Elf64Traits)
required init(source: ImageSource,
Expand Down Expand Up @@ -1222,11 +1224,21 @@ final class ElfImage<SomeElfTraits: ElfTraits>

var phdrs: [Traits.Phdr] = []
var phAddr = ImageSource.Address(header.e_phoff)
var minAddr: Traits.Address? = nil
for _ in 0..<header.e_phnum {
let phdr = maybeSwap(try source.fetch(from: phAddr, as: Traits.Phdr.self))
phdrs.append(phdr)
phAddr += ImageSource.Address(header.e_phentsize)

if phdr.p_type == .PT_LOAD {
if let oldMinAddr = minAddr {
minAddr = min(oldMinAddr, phdr.p_vaddr)
} else {
minAddr = phdr.p_vaddr
}
}
}
imageBase = ImageSource.Address(exactly: minAddr ?? 0)!
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Is there any benefit to failing gracefully here for values that aren't representable, like minAddr.map { ImageSource.Address(exactly: $0) } ?? 0?

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Not sure. On the one hand, that would stop it crashing in such a case. On the other, I think that's rather unlikely in practice (ImageSource.Address is usually UInt64).

programHeaders = phdrs

if source.isMappedImage {
Expand Down
9 changes: 6 additions & 3 deletions stdlib/public/RuntimeModule/SymbolicatedBacktrace.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -466,9 +466,6 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
for frame in backtrace.frames {
let address = frame.adjustedProgramCounter
if let imageNdx = theImages.indexOfImage(at: address) {
let relativeAddress = ImageSource.Address(
address - theImages[imageNdx].baseAddress
)
let name = theImages[imageNdx].name ?? "<unknown>"
var symbol: Symbol = Symbol(imageIndex: imageNdx,
imageName: name,
Expand Down Expand Up @@ -527,13 +524,19 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
if let hit = cache.lookup(path: theImages[imageNdx].path) {
switch hit {
case let .elf32Image(image):
let relativeAddress = ImageSource.Address(
address - theImages[imageNdx].baseAddress
) + image.imageBase
if let theSymbol = lookupSymbol(image: image,
at: imageNdx,
named: name,
address: relativeAddress) {
symbol = theSymbol
}
case let .elf64Image(image):
let relativeAddress = ImageSource.Address(
address - theImages[imageNdx].baseAddress
) + image.imageBase
if let theSymbol = lookupSymbol(image: image,
at: imageNdx,
named: name,
Expand Down
47 changes: 35 additions & 12 deletions stdlib/public/runtime/CrashHandlerLinux.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,15 @@
#include <string.h>
#include <unistd.h>

#define DEBUG_MEMSERVER 0

#if DEBUG_MEMSERVER
#include <stdio.h>
#define memserver_error(x) perror(x)
#else
#define memserver_error(x)
#endif

#include "swift/Runtime/Backtrace.h"

#include <cstring>
Expand Down Expand Up @@ -86,8 +95,8 @@ ssize_t safe_read(int fd, void *buf, size_t len) {
ssize_t ret;
do {
ret = read(fd, buf, len);
} while (ret < 0 && errno == EINTR);
if (ret < 0)
} while (ret <= 0 && errno == EINTR);
if (ret <= 0)
return ret;
total += ret;
ptr += ret;
Expand All @@ -106,8 +115,8 @@ ssize_t safe_write(int fd, const void *buf, size_t len) {
ssize_t ret;
do {
ret = write(fd, buf, len);
} while (ret < 0 && errno == EINTR);
if (ret < 0)
} while (ret <= 0 && errno == EINTR);
if (ret <= 0)
return ret;
total += ret;
ptr += ret;
Expand Down Expand Up @@ -657,20 +666,28 @@ memserver_start()
int fds[2];

ret = socketpair(AF_UNIX, SOCK_STREAM, 0, fds);
if (ret < 0)
if (ret < 0) {
memserver_error("memserver_start: socketpair failed");
return ret;
}

memserver_fd = fds[0];
ret = clone(memserver_entry, memserver_stack + sizeof(memserver_stack),
#if MEMSERVER_USE_PROCESS
0,
#else
CLONE_THREAD | CLONE_VM | CLONE_FILES
| CLONE_FS | CLONE_IO | CLONE_SIGHAND,
#ifndef __musl__
// Can't use CLONE_THREAD on musl because the clone() function
// there returns EINVAL if we do.
CLONE_THREAD | CLONE_SIGHAND |
#endif
CLONE_VM | CLONE_FILES | CLONE_FS | CLONE_IO,
#endif
NULL);
if (ret < 0)
if (ret < 0) {
memserver_error("memserver_start: clone failed");
return ret;
}

#if MEMSERVER_USE_PROCESS
memserver_pid = ret;
Expand Down Expand Up @@ -718,7 +735,7 @@ memserver_entry(void *dummy __attribute__((unused))) {
int fd = memserver_fd;
int result = 1;

#if MEMSERVER_USE_PROCESS
#if MEMSERVER_USE_PROCESS || defined(__musl__)
prctl(PR_SET_NAME, "[backtrace]");
#endif

Expand All @@ -743,8 +760,10 @@ memserver_entry(void *dummy __attribute__((unused))) {
ssize_t ret;

ret = safe_read(fd, &req, sizeof(req));
if (ret != sizeof(req))
if (ret != sizeof(req)) {
memserver_error("memserver: terminating because safe_read() returned wrong size");
break;
}

uint64_t addr = req.addr;
uint64_t bytes = req.len;
Expand All @@ -761,15 +780,19 @@ memserver_entry(void *dummy __attribute__((unused))) {
resp.len = ret;

ret = safe_write(fd, &resp, sizeof(resp));
if (ret != sizeof(resp))
if (ret != sizeof(resp)) {
memserver_error("memserver: terminating because safe_write() failed");
goto fail;
}

if (resp.len < 0)
break;

ret = safe_write(fd, memserver_buffer, resp.len);
if (ret != resp.len)
if (ret != resp.len) {
memserver_error("memserver: terminating because safe_write() failed (2)");
goto fail;
}

addr += resp.len;
bytes -= resp.len;
Expand Down