[glibc] Fix gen-as-const-headers races with the parallel subdir recursion (BZ 34438)

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=60c9ed0e6b9cce07e85ee56fc39b9afe36919e45

commit 60c9ed0e6b9cce07e85ee56fc39b9afe36919e45
Author: Adhemerval Zanella <[email protected]>
Date:   Thu Aug 6 14:07:55 2026 -0300

    Fix gen-as-const-headers races with the parallel subdir recursion (BZ 34438)
    
    The parallel subdirectory recursion (commit 7cac99621e96) only orders
    csu (and mach/hurd on Hurd) before the parallel fan-out plus the edges
    the Depend files request.  A header generated from gen-as-const-headers
    is only ordered before the compilations of the subdirectory that
    adds the .sym (through before-compile), so a header consumed by a
    different subdirectory may not exist yet when its consumer is
    compiled.
    
    That is the case for <sigaltstack-offsets.h>: it is generated when
    building misc, while its only consumer, ____longjmp_chk.S (x86_64 and
    sh), is built in debug.  The serial recursion always ran misc before
    debug in the sorted order, hiding the missing dependency.
    
    Move the generate the header to 'debug' instead.
    
    The same class of problem exists on Hurd: jmp_buf-ssp.h that is used
    by ____longjmp_chk.S in debug, and signal-defines.h that is sued
    by debug and setjmp.
    
    Deterministically reproduced with 'make debug/subdir_lib' from a clean
    build tree (which orders only csu before debug), and verified with
    builds for x86_64-linux-gnu, sh4-linux-gnu, i686-gnu, and x86_64-gnu.
    Reviewed-by: Sam James <[email protected]>

Diff:
---
 Makerules                               | 12 +++++++++++-
 sysdeps/mach/hurd/x86/Makefile          |  6 +-----
 sysdeps/unix/sysv/linux/sh/Makefile     |  4 +++-
 sysdeps/unix/sysv/linux/x86_64/Makefile |  4 +++-
 sysdeps/x86/Makefile                    | 10 ++++++++--
 5 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/Makerules b/Makerules
index 6bef57ece9..cef30974f1 100644
--- a/Makerules
+++ b/Makerules
@@ -259,7 +259,17 @@ endif  # gen-py-const-headers
 ifdef gen-as-const-headers
 # Generating headers for assembly constants.
 # We need this defined early to get into before-compile before
-# it's used in sysd-rules, below.
+# it's used in sysd-rules, below.  The gen-as-const-headers is evaluated
+# per subdirectory, so the before-compile dependency below only orders
+# the generated header before the compiles of the subdirectory whose
+# Makefile adds the .sym directive.
+# The parallel subdirectory recursion does not order sibling subdirectories,
+# so a .sym must be added in the subdirectory that compiles its consumers,
+# or in csu (which runs before the parallel) when it has consumers in
+# several subdirectories.
+# It must not add the same .sym in several subdirectories though: their
+# concurrent sub-makes would race generating the header through the fixed
+# temporary files below.
 # Define GEN_AS_CONST_HEADERS to avoid circular dependency [BZ #22792].
 # NB: <tcb-offsets.h> is generated from tcb-offsets.sym to define
 # offsets and sizes of types in <tls.h> and maybe <pthread.h> which
diff --git a/sysdeps/mach/hurd/x86/Makefile b/sysdeps/mach/hurd/x86/Makefile
index 97e3287c87..1d94f3a1c1 100644
--- a/sysdeps/mach/hurd/x86/Makefile
+++ b/sysdeps/mach/hurd/x86/Makefile
@@ -3,11 +3,7 @@ sysdep_routines += ioperm
 sysdep_headers += sys/io.h
 endif
 
-ifeq ($(subdir),debug)
-gen-as-const-headers += signal-defines.sym
-endif
-
-ifeq ($(subdir),setjmp)
+ifeq ($(subdir),csu)
 gen-as-const-headers += signal-defines.sym
 endif
 
diff --git a/sysdeps/unix/sysv/linux/sh/Makefile b/sysdeps/unix/sysv/linux/sh/Makefile
index dd3b382ac1..8c4cb73824 100644
--- a/sysdeps/unix/sysv/linux/sh/Makefile
+++ b/sysdeps/unix/sysv/linux/sh/Makefile
@@ -6,7 +6,9 @@ ifeq ($(subdir),stdlib)
 gen-as-const-headers += ucontext_i.sym
 endif
 
-ifeq ($(subdir),misc)
+# <sigaltstack-offsets.h> is only used by ____longjmp_chk.S, which is
+# built in the debug subdirectory.
+ifeq ($(subdir),debug)
 gen-as-const-headers += sigaltstack-offsets.sym
 endif
 
diff --git a/sysdeps/unix/sysv/linux/x86_64/Makefile b/sysdeps/unix/sysv/linux/x86_64/Makefile
index 6938382801..528fd951b2 100644
--- a/sysdeps/unix/sysv/linux/x86_64/Makefile
+++ b/sysdeps/unix/sysv/linux/x86_64/Makefile
@@ -10,7 +10,9 @@ ifeq ($(subdir),csu)
 gen-as-const-headers += ucontext_i.sym
 endif
 
-ifeq ($(subdir),misc)
+# <sigaltstack-offsets.h> is only used by ____longjmp_chk.S, which is
+# built in the debug subdirectory.
+ifeq ($(subdir),debug)
 gen-as-const-headers += sigaltstack-offsets.sym
 endif
 
diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
index 232e388d32..b4434deb0c 100644
--- a/sysdeps/x86/Makefile
+++ b/sysdeps/x86/Makefile
@@ -1,5 +1,12 @@
 ifeq ($(subdir),csu)
-gen-as-const-headers += cpu-features-offsets.sym features-offsets.sym
+# <jmp_buf-ssp.h> is used by the setjmp/longjmp implementations in the
+# setjmp subdirectory and also by ____longjmp_chk.S in the debug
+# subdirectory.
+gen-as-const-headers += \
+  cpu-features-offsets.sym \
+  features-offsets.sym \
+  jmp_buf-ssp.sym \
+  # gen-as-const-headers
 endif
 
 ifeq ($(subdir),elf)
@@ -171,7 +178,6 @@ tests += \
 endif # $(subdir) == math
 
 ifeq ($(subdir),setjmp)
-gen-as-const-headers += jmp_buf-ssp.sym
 sysdep_routines += __longjmp_cancel
 endif