[Xen-devel] [PATCH v3 15/18] bug/x86/arm: Align bug_frames sections.

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

Most of the WARN_ON or BUG_ON sections are properly aligned on
x86. However on ARM and on x86 assembler the macros don't include
any aligment information - hence they end up being the default
byte granularity.

On ARM32 it is paramount that the aligment is word-size (4)
otherwise if one tries to use (uint32_t*) access (such
as livepatch ELF relocations) we get a Data Abort.

Enforcing bug_frames to have the proper aligment across all
architectures and in both C and x86 makes them all the same.

Furthermore on x86 the bloat-o-meter detects that with this
change:

[konrad@char xen]$ ~/linux/scripts/bloat-o-meter xen-syms xen-syms.align4
add/remove: 0/0 grow/shrink: 3/14 up/down: 115/-1497 (-1382)
function                                     old     new   delta
mod_l1_entry                                1490    1587     +97
p2m_switch_domain_altp2m_by_id               520     533     +13
p2m_switch_vcpu_altp2m_by_id                 453     458      +5
machine_kexec                                263     261      -2
hvm_do_IRQ_dpci                              244     242      -2
sh_page_fault__guest_4                      8252    8192     -60
sh_audit_gw                                 1529    1462     -67
validate_gl3e                                337     264     -73
validate_gl4e                                449     375     -74
p2m_altp2m_lazy_copy                         730     652     -78
set_typed_p2m_entry                         1346    1259     -87
virt_to_xen_l2e                              491     365    -126
sh_x86_emulate_write__guest_4                443     288    -155
p2m_mem_access_check                        1733    1576    -157
sh_x86_emulate_cmpxchg__guest_4              512     349    -163
__get_gfn_type_access                        709     542    -167
map_pages_to_xen                            4430    4144    -286
Total: Before=1974033, After=1972651, chg -0.07%

We end up making the binary file a bit smaller.

On ARM32:
add/remove: 1/0 grow/shrink: 0/1 up/down: 384/-288 (96)
function                                     old     new   delta
gnttab_unpopulate_status_frames                -     384    +384
do_grant_table_op                          10808   10520    -288

And ARM64:
add/remove: 1/2 grow/shrink: 0/1 up/down: 4164/-4236 (-72)
function                                     old     new   delta
gnttab_map_grant_ref                           -    4164   +4164
do_grant_table_op                           9892    9836     -56
grant_map_exists                             300       -    -300
__gnttab_map_grant_ref                      3880       -   -3880

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>

v3: First submission. Replaces the "livepatch/elf: Adjust section aligment to 
word"
    patch.
---
 xen/include/asm-arm/bug.h | 1 +
 xen/include/asm-x86/bug.h | 1 +
 2 files changed, 2 insertions(+)

diff --git a/xen/include/asm-arm/bug.h b/xen/include/asm-arm/bug.h
index 68353e1..773d63e 100644
--- a/xen/include/asm-arm/bug.h
+++ b/xen/include/asm-arm/bug.h
@@ -52,6 +52,7 @@ struct bug_frame {
          ".popsection\n"                                                    \
          ".pushsection .bug_frames." __stringify(type) ", \"a\", %progbits\n"\
          "4:\n"                                                             \
+         ".align 4\n"                                                       \
          ".long (1b - 4b)\n"                                                \
          ".long (2b - 4b)\n"                                                \
          ".long (3b - 4b)\n"                                                \
diff --git a/xen/include/asm-x86/bug.h b/xen/include/asm-x86/bug.h
index c5d2d4c..9bb4a19 100644
--- a/xen/include/asm-x86/bug.h
+++ b/xen/include/asm-x86/bug.h
@@ -98,6 +98,7 @@ extern const struct bug_frame __start_bug_frames[],
     .popsection
 
     .pushsection .bug_frames.\type, "a", @progbits
+        .p2align 2
         .L\@bf:
         .long (.L\@ud - .L\@bf) + \
                ((\line >> BUG_LINE_LO_WIDTH) << BUG_DISP_WIDTH)
-- 
2.4.11


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel