[Xen-devel] [PATCH v2 19/20] livepatch/elf: Adjust section aligment to word

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On most architectures it does not matter what the aligment is.

On ARM32 it is paramount that the aligment is word-size (4)
otherwise we get a Data Abort when trying to perform ELF
relocations. That is due to ARM 32 only being able to write to
word-aligned addresses.

The default section alignments for .bug.frame, .livepatch.depends,
,.rodata.str1, and .strtab are 1 unless we:

 - Provide our own linker script file.
 - Piggyback on Xen's (but that means lots of #ifdefery)
 - Throw an error and refuse the payload

Or just fix it up.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

v2: First submission
---
 xen/common/livepatch_elf.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c
index cda9b27..2392bdf 100644
--- a/xen/common/livepatch_elf.c
+++ b/xen/common/livepatch_elf.c
@@ -71,7 +71,15 @@ static int elf_resolve_sections(struct livepatch_elf *elf, 
const void *data)
         delta = elf->hdr->e_shoff + i * elf->hdr->e_shentsize;
 
         sec[i].sec = data + delta;
-
+        /*
+         * Some architectures REQUIRE section alignment to be word-size.
+         */
+        if ( sec[i].sec->sh_addralign % sizeof(uint32_t) )
+        {
+            dprintk(XENLOG_DEBUG, LIVEPATCH "%s: Adjusting aligment for 
section [%u]\n",
+                    elf->name, i);
+            ((Elf_Shdr *)sec[i].sec)->sh_addralign = 4;
+        }
         delta = sec[i].sec->sh_offset;
         /*
          * N.B. elf_resolve_section_names, elf_get_sym skip this check as
-- 
2.4.11


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