Re: [PATCH v2 1/6] Fix gen-as-const-headers races with the parallel subdir recursion (BZ 34438)

Sam James <[email protected]> Thu, 06 Aug 2026 19:02:38 +0100
Newsgroups	gmane.comp.lib.glibc.alpha
Organization	Gentoo
Message-ID	<[email protected]>
Adhemerval Zanella <[email protected]> writes:

> 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]>

> ---
>  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 6bef57ece93..cef30974f15 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 97e3287c873..1d94f3a1c16 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 ($(subdir),csu)
>  gen-as-const-headers += signal-defines.sym
>  endif
>  
> diff --git a/sysdeps/unix/sysv/linux/sh/Makefile b/sysdeps/unix/sysv/linux/sh/Makefile
> index dd3b382ac10..8c4cb73824f 100644
> --- a/sysdeps/unix/sysv/linux/sh/Makefile
> +++ b/sysdeps/unix/sysv/linux/sh/Makefile
> @@ -6,7 +6,9 @@ ifeq ($(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 6938382801f..528fd951b2d 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 ($(subdir),debug)
>  gen-as-const-headers += sigaltstack-offsets.sym
>  endif
>  
> diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
> index 232e388d325..b4434deb0c3 100644
> --- a/sysdeps/x86/Makefile
> +++ b/sysdeps/x86/Makefile
> @@ -1,5 +1,12 @@
>  ifeq ($(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
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