Fibers are broken on alpine x86 with clang

Description

Found while looking at #9735 (comment)

Most fibers tests fail when building with clang on alpine x86 in non-debug.

This Dockerfile allows to reproduce the issue:

FROM i386/alpine:3.17.1
RUN apk add gcc clang autoconf make bison re2c git musl-dev
RUN git clone  https://github.com/php/php-src --branch master --depth 1
WORKDIR php-src
RUN ./buildconf --force && \
    CC=clang \
    CXX=clang++ \
    ./configure --disable-all --with-pic --build i586-alpine-linux-musl && \
    make -j$(nproc)
RUN TESTS=Zend/tests/fibers make test || true
CMD bash

Also happens in an alpine VM:

CC=clang CXX=clang++ ./configure --disable-all
TESTS=Zend/tests/fibers make test

Tests pass when building with gcc, or with -O0.

PHP Version

8.1 f673449

Operating System

Alpine 3.17.1 x86

May be related: #9566

Thank you for filing issue. Sadly I have no idea how to tackle it

FYI I'm building only PHP 8.2 with clang, php81 package using gcc

I'm taking a brief look at this, it's a segfault in zend_fibers.c:350:

php-src/Zend/zend_fibers.c

Line 350 in 3ed5264

zend_fiber_transfer transfer = *data.transfer;

The problem seems to be in how the pointers (that are in the argument's struct) are passed from the assembly to the function.

The following patch fixes it for me. I guess more platforms than just Alpine are actually affected by this:

diff --git a/Zend/asm/make_i386_sysv_elf_gas.S b/Zend/asm/make_i386_sysv_elf_gas.S
index b76de260..5568f57b 100644
--- a/Zend/asm/make_i386_sysv_elf_gas.S
+++ b/Zend/asm/make_i386_sysv_elf_gas.S
@@ -82,8 +82,8 @@ make_fcontext:
 
 trampoline:
     /* move transport_t for entering context-function */
-    movl  %edi, (%esp)
-    movl  %esi, 0x4(%esp)
+    pushl %esi
+    pushl %edi
     pushl %ebp
     /* jump to context-function */
     jmp *%ebx

Can someone else please also verify if this fixes it for them? Thanks :)

Note: idk why the stack overwriting was used instead of pushing, I guess to save stack space? If that's the case we can do that too but the solution becomes a little more complicated.

I don't have a Linux 32-bit install handy, and I want to check whether it breaks other platforms or not. So I'm going to create a draft PR so that CI can run through this.

EDIT: oh also, I guess if this fix works then we can get rid of the fiber tests in that ignorelist you mentioned here: #9735 (comment) ?

Sync boost/context assembly files for fibers

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Fibers are broken on alpine x86 with clang #10398

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Fibers are broken on alpine x86 with clang #10398

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arnaud-lb commented on Jan 21, 2023

andypost commented on Jan 21, 2023

andypost commented on Jan 21, 2023

ndossche commented on Jan 21, 2023

ndossche commented on Jan 21, 2023

ndossche commented on Jan 21, 2023

ndossche commented on Jan 21, 2023

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