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armhf binaries still use NEON #36913
Description
I was just investigating a report that Fedora's rust binaries for armv7hl use NEON, but they should not per #35590, supposedly fixed in #35814. (Fedora's build is 1.11, but I applied that patch.) I can see the exact same issue in the latest official rustc-nightly-armv7-unknown-linux-gnueabihf.tar.gz, whose version file says 1.14.0-nightly (289f3a4ca 2016-09-29).
# arm-linux-gnu-objdump -d libstd-*.so | grep '<.*lang_start.*>:' -A30
0006ccf0 <_ZN3std2rt10lang_start17hdfc48bc748089cb2E>:
6ccf0: e92d4ff0 push {r4, r5, r6, r7, r8, r9, sl, fp, lr}
6ccf4: e24ddf45 sub sp, sp, #276 ; 0x114
6ccf8: e1a09001 mov r9, r1
6ccfc: e1a0b000 mov fp, r0
6cd00: e3a0000d mov r0, #13
6cd04: e3a01001 mov r1, #1
6cd08: e1a0a002 mov sl, r2
6cd0c: ebff5534 bl 421e4 <signal@plt>
6cd10: e3700001 cmn r0, #1
6cd14: 0a000134 beq 6d1ec <_ZN3std2rt10lang_start17hdfc48bc748089cb2E+0x4fc>
6cd18: e59f0788 ldr r0, [pc, #1928] ; 6d4a8 <_ZN3std2rt10lang_start17hdfc48bc748089cb2E+0x7b8>
6cd1c: e08f0000 add r0, pc, r0
6cd20: ebff5856 bl 42e80 <_ZN5alloc3oom15set_oom_handler17hfc02679a00c1734eE@plt>
6cd24: e3a0001e mov r0, #30
6cd28: ebff5509 bl 42154 <sysconf@plt>
6cd2c: e1a07000 mov r7, r0
6cd30: e28d0050 add r0, sp, #80 ; 0x50
6cd34: f2c00050 vmov.i32 q8, #0 ; 0x00000000
6cd38: e3a06000 mov r6, #0
6cd3c: e1a01000 mov r1, r0
6cd40: f4410acd vst1.64 {d16-d17}, [r1]!
6cd44: f4410acf vst1.64 {d16-d17}, [r1]
6cd48: e58d6070 str r6, [sp, #112] ; 0x70
6cd4c: ebff57d1 bl 42c98 <pthread_attr_init@plt>
6cd50: e59f1754 ldr r1, [pc, #1876] ; 6d4ac <_ZN3std2rt10lang_start17hdfc48bc748089cb2E+0x7bc>
6cd54: e28d8c01 add r8, sp, #256 ; 0x100
6cd58: e58d0100 str r0, [sp, #256] ; 0x100
6cd5c: e3500000 cmp r0, #0
6cd60: e58d80f4 str r8, [sp, #244] ; 0xf4
6cd64: e08f1001 add r1, pc, r1
In particular, they flagged that vmov.i32 q8, #0 as a problem. I'm no ARM expert, but from this it appears the qN registers are NEON-only. I believe those instructions using {d16-d17} are also a problem, because with VFP3-D16 we should only have d0 to d15.
Activity
alexcrichton commentedon Oct 3, 2016
Hm looks like it's definitely still there:
cuviper commentedon Oct 3, 2016
( TIL of
rustc +nightly! 😮 )rustc: Try again to disable NEON on armv7 linux
Auto merge of #36933 - alexcrichton:less-neon-again, r=eddyb
cuviper commentedon Oct 6, 2016
Just to confirm:
No
neon. This doesn't explicitly mentiond16vs.d32though.I ran
objdump -don all binaries inrustc-nightly-armv7-unknown-linux-gnueabihf.tar.gz. I see no mention of NEONqNregisters. I see uses ofd0-d15, but no higher, so I think+d16is OK too.I'll know better if someone with a limited armv7 actually tries to run this, but LGTM! ✔️
alexcrichton commentedon Oct 6, 2016
Thanks for the confirmation @cuviper!