[Bug 1729850] Re: artful openssl FTBFS on armhf

[Chris Coulson]

On the broken build, the first thing to notice is that when entering
sha256_block_data_order, we are running in Thumb mode, as bit 5 of the
status register is set:

(gdb) info registers                                
r0             0x4b7558 4945240                     
r1             0x4b7580 4945280                     
r2             0x1      1                           
r3             0x0      0                           
r4             0x4b7558 4945240                     
r5             0xfffef44c       4294898764          
r6             0x0      0                           
r7             0x4b7580 4945280                     
r8             0x3      3                           
r9             0xfffef44c       4294898764          
r10            0x0      0                           
r11            0x0      0                           
r12            0x0      0                           
sp             0xfffef3b8       0xfffef3b8          
lr             0x414387 4277127                     
pc             0x4160c0 0x4160c0 <sha256_block_data_order>                                               
cpsr           0x40080030       1074266160

The good build was not running in Thumb mode. sha256-armv4.S enables
Thumb instructions if __thumb2__ is defined by the compiler, see:

.text
#if __ARM_ARCH__<7
.code   32
#else
.syntax unified
# ifdef __thumb2__
.thumb
# else
.code   32
# endif
#endif

Sure enough, there's a difference between the 2 tested gcc builds.

Bad build:
$ gcc -dM -E - < /dev/null | grep __thumb2__
#define __thumb2__ 1
$

Good build:
$ gcc -dM -E - < /dev/null | grep __thumb2__
$

Looking in the changelog for gcc-7, I see the following comment for 7.2.0-2:
  * Restore configuring with --with-mode=thumb on armhf. Closes: #873584.

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https://bugs.launchpad.net/bugs/1729850

Title:
  artful openssl FTBFS on armhf

Status in binutils package in Ubuntu:
  New
Status in gcc-7 package in Ubuntu:
  New
Status in openssl package in Ubuntu:
  New

Bug description:
  openssl FTBFS on artful armhf with the following:

  ../util/shlib_wrap.sh ./sha256t
  Testing SHA-256 
  TEST 1 of 3 failed.

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