Re: Buildbot failure in Wildebeest Builder on whole buildset

[Mark Wielaard <mark@klomp.org>]

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On Tue, 2018-11-13 at 18:29 +0100, Mark Wielaard wrote:
> So we might actually have two bugs. 1) we don't handle incorrectly
> aligned compressed sections and 2) we generate such incorrectly
> aligned compressed sections ourselves.
> 
> Pondering fixes.

The fixes were easy!
(Hopefully the buildbot agrees.)
I pushed the attached.

Cheers,

Mark

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From cf10453f8252df81225796d98548ba6eac113df3 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mark@klomp.org>
Date: Tue, 13 Nov 2018 21:18:09 +0100
Subject: [PATCH] libelf: Correctly setup alignment of SHF_COMPRESSED section
 data.

We didn't set the alignment of SHF_COMPRESSED sections correctly.
Those sections start with an Elf(32|64)_Chdr. Make sure sh_addralign
is setup to be able to read such a struct directly. Likewise don't
trust the alignment set on any SHF_COMPRESSED section, but always
make the (raw) compressed data aligned correctly for the reading the
Elf(32|64)_Chdr directly.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 libelf/ChangeLog      |  7 +++++++
 libelf/elf_compress.c |  4 ++--
 libelf/elf_getdata.c  | 10 ++++++++--
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/libelf/ChangeLog b/libelf/ChangeLog
index ab078cb..93820d1 100644
--- a/libelf/ChangeLog
+++ b/libelf/ChangeLog
@@ -1,3 +1,10 @@
+2018-11-13  Mark Wielaard  <mark@klomp.org>
+
+	* elf_getdata.c (__libelf_set_rawdata_wrlock): Explicitly set the
+	alignment of SHF_COMPRESSED data to the alignment of ELF_T_CHDR.
+	* elf_compress.c (elf_compress): After compression set sh_addralign
+	to the alignment of ELF_T_CHDR.
+
 2018-11-09  Mark Wielaard  <mark@klomp.org>
 
 	* elf_compress_gnu.c (elf_compress_gnu): Use elf_getdata.
diff --git a/libelf/elf_compress.c b/libelf/elf_compress.c
index d96245d..be9eeab 100644
--- a/libelf/elf_compress.c
+++ b/libelf/elf_compress.c
@@ -455,14 +455,14 @@ elf_compress (Elf_Scn *scn, int type, unsigned int flags)
 	{
 	  Elf32_Shdr *shdr = elf32_getshdr (scn);
 	  shdr->sh_size = new_size;
-	  shdr->sh_addralign = 1;
+	  shdr->sh_addralign = __libelf_type_align (ELFCLASS32, ELF_T_CHDR);
 	  shdr->sh_flags |= SHF_COMPRESSED;
 	}
       else
 	{
 	  Elf64_Shdr *shdr = elf64_getshdr (scn);
 	  shdr->sh_size = new_size;
-	  shdr->sh_addralign = 1;
+	  shdr->sh_addralign = __libelf_type_align (ELFCLASS64, ELF_T_CHDR);
 	  shdr->sh_flags |= SHF_COMPRESSED;
 	}
 
diff --git a/libelf/elf_getdata.c b/libelf/elf_getdata.c
index 2043bba..639a798 100644
--- a/libelf/elf_getdata.c
+++ b/libelf/elf_getdata.c
@@ -268,9 +268,15 @@ __libelf_set_rawdata_wrlock (Elf_Scn *scn)
       /* First a test whether the section is valid at all.  */
       size_t entsize;
 
-      /* Compressed data has a header, but then compressed data.  */
+      /* Compressed data has a header, but then compressed data.
+	 Make sure to set the alignment of the header explicitly,
+	 don't trust the file alignment for the section, it is
+	 often wrong.  */
       if ((flags & SHF_COMPRESSED) != 0)
-	entsize = 1;
+	{
+	  entsize = 1;
+	  align = __libelf_type_align (elf->class, ELF_T_CHDR);
+	}
       else if (type == SHT_HASH)
 	{
 	  GElf_Ehdr ehdr_mem;
-- 
1.8.3.1