[PATCH v2 1/6] 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.
---
 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
 
-- 
2.53.0