* [PATCH] arm64/crypto: remove non-standard notation
@ 2018-08-20 22:40 Nick Desaulniers
2018-08-20 22:43 ` Nick Desaulniers
` (2 more replies)
0 siblings, 3 replies; 8+ messages in thread
From: Nick Desaulniers @ 2018-08-20 22:40 UTC (permalink / raw)
To: ard.biesheuvel
Cc: Nick Desaulniers, Herbert Xu, David S. Miller, Catalin Marinas,
Will Deacon, linux-crypto, linux-arm-kernel, linux-kernel
It seems that:
ldr q8, =0x30000000200000001
is a GNU as convience notation for:
ldr q8, .Lconstant
.Lconstant
.word 0x00000001
.word 0x00000002
.word 0x00000003
.word 0x00000000
based on this comment in binutils' source [0]. I've asked for this
non-standard convience notation to be added to other assemblers [1], but
until then, we can remove it and get equivalent disassembly:
before:
00000000000009d4 <neon_aes_ctr_encrypt>:
...
a48: 9c000ac8 ldr q8, ba0 <neon_aes_ctr_encrypt+0x1cc>
...
ba0: 00000001 .word 0x00000001
ba4: 00000002 .word 0x00000002
ba8: 00000003 .word 0x00000003
bac: 00000000 .word 0x00000000
after:
00000000000009d4 <neon_aes_ctr_encrypt>:
...
a48: 9c000aa8 ldr q8, b9c <neon_aes_ctr_encrypt+0x1c8>
...
b9c: 00000001 .word 0x00000001
ba0: 00000002 .word 0x00000002
ba4: 00000003 .word 0x00000003
ba8: 00000000 .word 0x00000000
[0] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gas/testsuite/gas/aarch64/programmer-friendly.s;h=6254c6476efdc848648b05068be0574e7addc85d;hb=HEAD#l11
[1] https://bugs.llvm.org/show_bug.cgi?id=38642
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
arch/arm64/crypto/aes-modes.S | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S
index 483a7130cf0e..9288c5b0eca2 100644
--- a/arch/arm64/crypto/aes-modes.S
+++ b/arch/arm64/crypto/aes-modes.S
@@ -232,7 +232,7 @@ AES_ENTRY(aes_ctr_encrypt)
bmi .Lctr1x
cmn w6, #4 /* 32 bit overflow? */
bcs .Lctr1x
- ldr q8, =0x30000000200000001 /* addends 1,2,3[,0] */
+ ldr q8, .Laddends /* addends 1,2,3[,0] */
dup v7.4s, w6
mov v0.16b, v4.16b
add v7.4s, v7.4s, v8.4s
@@ -295,6 +295,12 @@ AES_ENTRY(aes_ctr_encrypt)
rev x7, x7
ins v4.d[0], x7
b .Lctrcarrydone
+
+.Laddends:
+ .word 0x00000001
+ .word 0x00000002
+ .word 0x00000003
+ .word 0x00000000
AES_ENDPROC(aes_ctr_encrypt)
.ltorg
--
2.18.0.865.gffc8e1a3cd6-goog
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH] arm64/crypto: remove non-standard notation 2018-08-20 22:40 [PATCH] arm64/crypto: remove non-standard notation Nick Desaulniers @ 2018-08-20 22:43 ` Nick Desaulniers 2018-08-21 0:04 ` Will Deacon 2018-08-21 12:23 ` Ard Biesheuvel 2 siblings, 0 replies; 8+ messages in thread From: Nick Desaulniers @ 2018-08-20 22:43 UTC (permalink / raw) To: Ard Biesheuvel Cc: Herbert Xu, David S. Miller, Catalin Marinas, Will Deacon, linux-crypto, Linux ARM, LKML On Mon, Aug 20, 2018 at 3:41 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > > It seems that: > ldr q8, =0x30000000200000001 > > is a GNU as convience notation for: > ldr q8, .Lconstant > .Lconstant > .word 0x00000001 > .word 0x00000002 > .word 0x00000003 > .word 0x00000000 > > based on this comment in binutils' source [0]. I've asked for this > non-standard convience notation to be added to other assemblers [1], but > until then, we can remove it and get equivalent disassembly: > > before: > 00000000000009d4 <neon_aes_ctr_encrypt>: > ... > a48: 9c000ac8 ldr q8, ba0 <neon_aes_ctr_encrypt+0x1cc> > ... > ba0: 00000001 .word 0x00000001 > ba4: 00000002 .word 0x00000002 > ba8: 00000003 .word 0x00000003 > bac: 00000000 .word 0x00000000 > > after: > > 00000000000009d4 <neon_aes_ctr_encrypt>: > ... > a48: 9c000aa8 ldr q8, b9c <neon_aes_ctr_encrypt+0x1c8> > ... > b9c: 00000001 .word 0x00000001 > ba0: 00000002 .word 0x00000002 > ba4: 00000003 .word 0x00000003 > ba8: 00000000 .word 0x00000000 > > [0] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gas/testsuite/gas/aarch64/programmer-friendly.s;h=6254c6476efdc848648b05068be0574e7addc85d;hb=HEAD#l11 > [1] https://bugs.llvm.org/show_bug.cgi?id=38642 > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > arch/arm64/crypto/aes-modes.S | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S > index 483a7130cf0e..9288c5b0eca2 100644 > --- a/arch/arm64/crypto/aes-modes.S > +++ b/arch/arm64/crypto/aes-modes.S > @@ -232,7 +232,7 @@ AES_ENTRY(aes_ctr_encrypt) > bmi .Lctr1x > cmn w6, #4 /* 32 bit overflow? */ > bcs .Lctr1x > - ldr q8, =0x30000000200000001 /* addends 1,2,3[,0] */ > + ldr q8, .Laddends /* addends 1,2,3[,0] */ > dup v7.4s, w6 > mov v0.16b, v4.16b > add v7.4s, v7.4s, v8.4s > @@ -295,6 +295,12 @@ AES_ENTRY(aes_ctr_encrypt) > rev x7, x7 > ins v4.d[0], x7 > b .Lctrcarrydone > + > +.Laddends: > + .word 0x00000001 > + .word 0x00000002 > + .word 0x00000003 > + .word 0x00000000 > AES_ENDPROC(aes_ctr_encrypt) > .ltorg > > -- > 2.18.0.865.gffc8e1a3cd6-goog > I can't spell. s/convience/convenience/g -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] arm64/crypto: remove non-standard notation 2018-08-20 22:40 [PATCH] arm64/crypto: remove non-standard notation Nick Desaulniers 2018-08-20 22:43 ` Nick Desaulniers @ 2018-08-21 0:04 ` Will Deacon 2018-08-21 12:23 ` Ard Biesheuvel 2 siblings, 0 replies; 8+ messages in thread From: Will Deacon @ 2018-08-21 0:04 UTC (permalink / raw) To: Nick Desaulniers Cc: ard.biesheuvel, Herbert Xu, David S. Miller, Catalin Marinas, linux-crypto, linux-arm-kernel, linux-kernel On Mon, Aug 20, 2018 at 03:40:32PM -0700, Nick Desaulniers wrote: > It seems that: > ldr q8, =0x30000000200000001 > > is a GNU as convience notation for: > ldr q8, .Lconstant > .Lconstant > .word 0x00000001 > .word 0x00000002 > .word 0x00000003 > .word 0x00000000 Does still this work correctly for a big-endian build? Will ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] arm64/crypto: remove non-standard notation 2018-08-20 22:40 [PATCH] arm64/crypto: remove non-standard notation Nick Desaulniers 2018-08-20 22:43 ` Nick Desaulniers 2018-08-21 0:04 ` Will Deacon @ 2018-08-21 12:23 ` Ard Biesheuvel 2018-08-21 16:50 ` Nick Desaulniers 2 siblings, 1 reply; 8+ messages in thread From: Ard Biesheuvel @ 2018-08-21 12:23 UTC (permalink / raw) To: Nick Desaulniers Cc: Herbert Xu, David S. Miller, Catalin Marinas, Will Deacon, open list:HARDWARE RANDOM NUMBER GENERATOR CORE, linux-arm-kernel, Linux Kernel Mailing List Hi Nick, On 21 August 2018 at 00:40, Nick Desaulniers <ndesaulniers@google.com> wrote: > It seems that: > ldr q8, =0x30000000200000001 > > is a GNU as convience notation for: > ldr q8, .Lconstant > .Lconstant > .word 0x00000001 > .word 0x00000002 > .word 0x00000003 > .word 0x00000000 > > based on this comment in binutils' source [0]. I've asked for this > non-standard convience notation to be added to other assemblers [1], but > until then, we can remove it and get equivalent disassembly: > What do you mean by 'non-standard convenience notation'? Which asm 'standard' does Clang actually claim to implement? This 'GCC/binutils is broken and we are reluctant to subvert Clang' attitude is getting a bit old tbh. In the future, could you please mention clang explicitly in the patch subject so it is obvious what the purpose of the patch is? I think we should accommodate Clang in Linux, but the attitude has got to go. > before: > 00000000000009d4 <neon_aes_ctr_encrypt>: > ... > a48: 9c000ac8 ldr q8, ba0 <neon_aes_ctr_encrypt+0x1cc> > ... > ba0: 00000001 .word 0x00000001 > ba4: 00000002 .word 0x00000002 > ba8: 00000003 .word 0x00000003 > bac: 00000000 .word 0x00000000 > > after: > > 00000000000009d4 <neon_aes_ctr_encrypt>: > ... > a48: 9c000aa8 ldr q8, b9c <neon_aes_ctr_encrypt+0x1c8> > ... > b9c: 00000001 .word 0x00000001 > ba0: 00000002 .word 0x00000002 > ba4: 00000003 .word 0x00000003 > ba8: 00000000 .word 0x00000000 > > [0] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gas/testsuite/gas/aarch64/programmer-friendly.s;h=6254c6476efdc848648b05068be0574e7addc85d;hb=HEAD#l11 > [1] https://bugs.llvm.org/show_bug.cgi?id=38642 > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > arch/arm64/crypto/aes-modes.S | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S > index 483a7130cf0e..9288c5b0eca2 100644 > --- a/arch/arm64/crypto/aes-modes.S > +++ b/arch/arm64/crypto/aes-modes.S > @@ -232,7 +232,7 @@ AES_ENTRY(aes_ctr_encrypt) > bmi .Lctr1x > cmn w6, #4 /* 32 bit overflow? */ > bcs .Lctr1x > - ldr q8, =0x30000000200000001 /* addends 1,2,3[,0] */ > + ldr q8, .Laddends /* addends 1,2,3[,0] */ > dup v7.4s, w6 > mov v0.16b, v4.16b > add v7.4s, v7.4s, v8.4s > @@ -295,6 +295,12 @@ AES_ENTRY(aes_ctr_encrypt) > rev x7, x7 > ins v4.d[0], x7 > b .Lctrcarrydone > + > +.Laddends: > + .word 0x00000001 > + .word 0x00000002 > + .word 0x00000003 > + .word 0x00000000 As Will points out, this breaks BE builds. > AES_ENDPROC(aes_ctr_encrypt) > .ltorg You can drop this .ltorg if you get rid of all =xxx instances. Actually, though, I would prefer it if we could use some clever short sequence of movi+add instructions, and get rid of the literal altogether. Or otherwise, please use something like ldr_l q8, .Laddends, <temp register> instead, and move the literal into the .rodata section (and use .octa so you don't break BE) ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] arm64/crypto: remove non-standard notation 2018-08-21 12:23 ` Ard Biesheuvel @ 2018-08-21 16:50 ` Nick Desaulniers 2018-08-21 17:00 ` Ard Biesheuvel 0 siblings, 1 reply; 8+ messages in thread From: Nick Desaulniers @ 2018-08-21 16:50 UTC (permalink / raw) To: Ard Biesheuvel Cc: Herbert Xu, David S. Miller, Catalin Marinas, Will Deacon, linux-crypto, Linux ARM, LKML On Tue, Aug 21, 2018 at 5:23 AM Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > > Hi Nick, > > On 21 August 2018 at 00:40, Nick Desaulniers <ndesaulniers@google.com> wrote: > > It seems that: > > ldr q8, =0x30000000200000001 > > > > is a GNU as convience notation for: > > ldr q8, .Lconstant > > .Lconstant > > .word 0x00000001 > > .word 0x00000002 > > .word 0x00000003 > > .word 0x00000000 > > > > based on this comment in binutils' source [0]. I've asked for this > > non-standard convience notation to be added to other assemblers [1], but > > until then, we can remove it and get equivalent disassembly: > > > > What do you mean by 'non-standard convenience notation'? Which asm > 'standard' does Clang actually claim to implement? Well, for assembly 'standard' is a bit nebulous. But it's frustrating when you can't find what the `=0x...` notation means in either the ARM or GNU as manuals. The source of truth happened to be a comment in the source [0] that explained that this was a "programmer friendly notation." Sure, if you can find it. > > This 'GCC/binutils is broken and we are reluctant to subvert Clang' > attitude is getting a bit old tbh. In the future, could you please > mention clang explicitly in the patch subject so it is obvious what > the purpose of the patch is? I think we should accommodate Clang in > Linux, but the attitude has got to go. 'Reluctant?' Please assume good faith; I filed the bug/noticed yesterday [1]. And I'm in favor of supporting the shorthand. That's not my argument at all; Strawman. > > > > before: > > 00000000000009d4 <neon_aes_ctr_encrypt>: > > ... > > a48: 9c000ac8 ldr q8, ba0 <neon_aes_ctr_encrypt+0x1cc> > > ... > > ba0: 00000001 .word 0x00000001 > > ba4: 00000002 .word 0x00000002 > > ba8: 00000003 .word 0x00000003 > > bac: 00000000 .word 0x00000000 > > > > after: > > > > 00000000000009d4 <neon_aes_ctr_encrypt>: > > ... > > a48: 9c000aa8 ldr q8, b9c <neon_aes_ctr_encrypt+0x1c8> > > ... > > b9c: 00000001 .word 0x00000001 > > ba0: 00000002 .word 0x00000002 > > ba4: 00000003 .word 0x00000003 > > ba8: 00000000 .word 0x00000000 > > > > [0] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gas/testsuite/gas/aarch64/programmer-friendly.s;h=6254c6476efdc848648b05068be0574e7addc85d;hb=HEAD#l11 > > [1] https://bugs.llvm.org/show_bug.cgi?id=38642 > > > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > --- > > arch/arm64/crypto/aes-modes.S | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S > > index 483a7130cf0e..9288c5b0eca2 100644 > > --- a/arch/arm64/crypto/aes-modes.S > > +++ b/arch/arm64/crypto/aes-modes.S > > @@ -232,7 +232,7 @@ AES_ENTRY(aes_ctr_encrypt) > > bmi .Lctr1x > > cmn w6, #4 /* 32 bit overflow? */ > > bcs .Lctr1x > > - ldr q8, =0x30000000200000001 /* addends 1,2,3[,0] */ > > + ldr q8, .Laddends /* addends 1,2,3[,0] */ > > dup v7.4s, w6 > > mov v0.16b, v4.16b > > add v7.4s, v7.4s, v8.4s > > @@ -295,6 +295,12 @@ AES_ENTRY(aes_ctr_encrypt) > > rev x7, x7 > > ins v4.d[0], x7 > > b .Lctrcarrydone > > + > > +.Laddends: > > + .word 0x00000001 > > + .word 0x00000002 > > + .word 0x00000003 > > + .word 0x00000000 > > As Will points out, this breaks BE builds. Looks like -EB and -EL are the flags for me to test with in GNU as (looks like a few different flags for this). Is there a target triple ABI for BE? I'll ask around here too, and post my findings. > > > AES_ENDPROC(aes_ctr_encrypt) > > .ltorg > > You can drop this .ltorg if you get rid of all =xxx instances. > > Actually, though, I would prefer it if we could use some clever short > sequence of movi+add instructions, and get rid of the literal > altogether. Or otherwise, please use something like > > ldr_l q8, .Laddends, <temp register> > > instead, and move the literal into the .rodata section (and use .octa > so you don't break BE) Ah, .octa, neat. Ok, I'll take a look for v2. -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] arm64/crypto: remove non-standard notation 2018-08-21 16:50 ` Nick Desaulniers @ 2018-08-21 17:00 ` Ard Biesheuvel 2018-08-21 17:25 ` Robin Murphy 0 siblings, 1 reply; 8+ messages in thread From: Ard Biesheuvel @ 2018-08-21 17:00 UTC (permalink / raw) To: Nick Desaulniers Cc: Herbert Xu, David S. Miller, Catalin Marinas, Will Deacon, open list:HARDWARE RANDOM NUMBER GENERATOR CORE, Linux ARM, LKML On 21 August 2018 at 18:50, Nick Desaulniers <ndesaulniers@google.com> wrote: > On Tue, Aug 21, 2018 at 5:23 AM Ard Biesheuvel > <ard.biesheuvel@linaro.org> wrote: >> >> Hi Nick, >> >> On 21 August 2018 at 00:40, Nick Desaulniers <ndesaulniers@google.com> wrote: >> > It seems that: >> > ldr q8, =0x30000000200000001 >> > >> > is a GNU as convience notation for: >> > ldr q8, .Lconstant >> > .Lconstant >> > .word 0x00000001 >> > .word 0x00000002 >> > .word 0x00000003 >> > .word 0x00000000 >> > >> > based on this comment in binutils' source [0]. I've asked for this >> > non-standard convience notation to be added to other assemblers [1], but >> > until then, we can remove it and get equivalent disassembly: >> > >> >> What do you mean by 'non-standard convenience notation'? Which asm >> 'standard' does Clang actually claim to implement? > > Well, for assembly 'standard' is a bit nebulous. But it's frustrating > when you can't find what the `=0x...` notation means in either the ARM > or GNU as manuals. The source of truth happened to be a comment in > the source [0] that explained that this was a "programmer friendly > notation." Sure, if you can find it. > Well, it is documented in the ARM manuals as the 'ldr pseudo instruction' for 32-bit ARM, and originally, it would only emit a literal if the value could not be loaded using a ordinary mov. For AArch64, I don't think that occurs any longer, i.e., a ldr is always emitted as an ldr. However, it is used widely in the ARM code (although not as much in arch/arm64) for loading compile time constants and even symbol addresses into general purpose registers. The FP variant may actually be a GNU invention, but given that there is no standard to begin with, playing the 'GNU is non-standard' card again is just a bit annoying. >> >> This 'GCC/binutils is broken and we are reluctant to subvert Clang' >> attitude is getting a bit old tbh. In the future, could you please >> mention clang explicitly in the patch subject so it is obvious what >> the purpose of the patch is? I think we should accommodate Clang in >> Linux, but the attitude has got to go. > > 'Reluctant?' Please assume good faith; I filed the bug/noticed > yesterday [1]. And I'm in favor of supporting the shorthand. That's > not my argument at all; Strawman. > OK, fair enough. But note that Clang already supports the syntax for GPRs. >> >> >> > before: >> > 00000000000009d4 <neon_aes_ctr_encrypt>: >> > ... >> > a48: 9c000ac8 ldr q8, ba0 <neon_aes_ctr_encrypt+0x1cc> >> > ... >> > ba0: 00000001 .word 0x00000001 >> > ba4: 00000002 .word 0x00000002 >> > ba8: 00000003 .word 0x00000003 >> > bac: 00000000 .word 0x00000000 >> > >> > after: >> > >> > 00000000000009d4 <neon_aes_ctr_encrypt>: >> > ... >> > a48: 9c000aa8 ldr q8, b9c <neon_aes_ctr_encrypt+0x1c8> >> > ... >> > b9c: 00000001 .word 0x00000001 >> > ba0: 00000002 .word 0x00000002 >> > ba4: 00000003 .word 0x00000003 >> > ba8: 00000000 .word 0x00000000 >> > >> > [0] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gas/testsuite/gas/aarch64/programmer-friendly.s;h=6254c6476efdc848648b05068be0574e7addc85d;hb=HEAD#l11 >> > [1] https://bugs.llvm.org/show_bug.cgi?id=38642 >> > >> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> >> > --- >> > arch/arm64/crypto/aes-modes.S | 8 +++++++- >> > 1 file changed, 7 insertions(+), 1 deletion(-) >> > >> > diff --git a/arch/arm64/crypto/aes-modes.S b/arch/arm64/crypto/aes-modes.S >> > index 483a7130cf0e..9288c5b0eca2 100644 >> > --- a/arch/arm64/crypto/aes-modes.S >> > +++ b/arch/arm64/crypto/aes-modes.S >> > @@ -232,7 +232,7 @@ AES_ENTRY(aes_ctr_encrypt) >> > bmi .Lctr1x >> > cmn w6, #4 /* 32 bit overflow? */ >> > bcs .Lctr1x >> > - ldr q8, =0x30000000200000001 /* addends 1,2,3[,0] */ >> > + ldr q8, .Laddends /* addends 1,2,3[,0] */ >> > dup v7.4s, w6 >> > mov v0.16b, v4.16b >> > add v7.4s, v7.4s, v8.4s >> > @@ -295,6 +295,12 @@ AES_ENTRY(aes_ctr_encrypt) >> > rev x7, x7 >> > ins v4.d[0], x7 >> > b .Lctrcarrydone >> > + >> > +.Laddends: >> > + .word 0x00000001 >> > + .word 0x00000002 >> > + .word 0x00000003 >> > + .word 0x00000000 >> > > >> As Will points out, this breaks BE builds. > > Looks like -EB and -EL are the flags for me to test with in GNU as > (looks like a few different flags for this). Is there a target triple > ABI for BE? I'll ask around here too, and post my findings. > >> >> > AES_ENDPROC(aes_ctr_encrypt) >> > .ltorg >> >> You can drop this .ltorg if you get rid of all =xxx instances. >> >> Actually, though, I would prefer it if we could use some clever short >> sequence of movi+add instructions, and get rid of the literal >> altogether. Or otherwise, please use something like >> >> ldr_l q8, .Laddends, <temp register> >> >> instead, and move the literal into the .rodata section (and use .octa >> so you don't break BE) > > Ah, .octa, neat. Ok, I'll take a look for v2. > Please check my solution first. I just sent it out. ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] arm64/crypto: remove non-standard notation 2018-08-21 17:00 ` Ard Biesheuvel @ 2018-08-21 17:25 ` Robin Murphy 2018-08-21 18:13 ` Nick Desaulniers 0 siblings, 1 reply; 8+ messages in thread From: Robin Murphy @ 2018-08-21 17:25 UTC (permalink / raw) To: Ard Biesheuvel, Nick Desaulniers Cc: Herbert Xu, Catalin Marinas, Will Deacon, LKML, open list:HARDWARE RANDOM NUMBER GENERATOR CORE, David S. Miller, Linux ARM On 21/08/18 18:00, Ard Biesheuvel wrote: > On 21 August 2018 at 18:50, Nick Desaulniers <ndesaulniers@google.com> wrote: >> On Tue, Aug 21, 2018 at 5:23 AM Ard Biesheuvel >> <ard.biesheuvel@linaro.org> wrote: >>> >>> Hi Nick, >>> >>> On 21 August 2018 at 00:40, Nick Desaulniers <ndesaulniers@google.com> wrote: >>>> It seems that: >>>> ldr q8, =0x30000000200000001 >>>> >>>> is a GNU as convience notation for: >>>> ldr q8, .Lconstant >>>> .Lconstant >>>> .word 0x00000001 >>>> .word 0x00000002 >>>> .word 0x00000003 >>>> .word 0x00000000 >>>> >>>> based on this comment in binutils' source [0]. I've asked for this >>>> non-standard convience notation to be added to other assemblers [1], but >>>> until then, we can remove it and get equivalent disassembly: >>>> >>> >>> What do you mean by 'non-standard convenience notation'? Which asm >>> 'standard' does Clang actually claim to implement? >> >> Well, for assembly 'standard' is a bit nebulous. But it's frustrating >> when you can't find what the `=0x...` notation means in either the ARM >> or GNU as manuals. The source of truth happened to be a comment in >> the source [0] that explained that this was a "programmer friendly >> notation." Sure, if you can find it. >> > > Well, it is documented in the ARM manuals as the 'ldr pseudo > instruction' for 32-bit ARM, and originally, it would only emit a > literal if the value could not be loaded using a ordinary mov. FWIW It's certainly well-documented by common A64 assemblers too: http://infocenter.arm.com/help/topic/com.arm.doc.100069_0610_01_en/dom1395139540926.html https://sourceware.org/binutils/docs/as/AArch64-Opcodes.html#AArch64-Opcodes > For AArch64, I don't think that occurs any longer, i.e., a ldr is > always emitted as an ldr. However, it is used widely in the ARM code > (although not as much in arch/arm64) for loading compile time > constants and even symbol addresses into general purpose registers. > The FP variant may actually be a GNU invention, but given that there > is no standard to begin with, playing the 'GNU is non-standard' card > again is just a bit annoying. I note that GAS just says "register" rather than explicitly calling out GPRs as armasm does, so in some ways it's not even all that unexpected that FP registers also work there, even if it is a bit funky. Robin. ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] arm64/crypto: remove non-standard notation 2018-08-21 17:25 ` Robin Murphy @ 2018-08-21 18:13 ` Nick Desaulniers 0 siblings, 0 replies; 8+ messages in thread From: Nick Desaulniers @ 2018-08-21 18:13 UTC (permalink / raw) To: Robin Murphy Cc: Ard Biesheuvel, Herbert Xu, Catalin Marinas, Will Deacon, LKML, linux-crypto, David S. Miller, Linux ARM On Tue, Aug 21, 2018 at 10:25 AM Robin Murphy <robin.murphy@arm.com> wrote: > > On 21/08/18 18:00, Ard Biesheuvel wrote: > > On 21 August 2018 at 18:50, Nick Desaulniers <ndesaulniers@google.com> wrote: > >> On Tue, Aug 21, 2018 at 5:23 AM Ard Biesheuvel > >> <ard.biesheuvel@linaro.org> wrote: > >>> > >>> Hi Nick, > >>> > >>> On 21 August 2018 at 00:40, Nick Desaulniers <ndesaulniers@google.com> wrote: > >>>> It seems that: > >>>> ldr q8, =0x30000000200000001 > >>>> > >>>> is a GNU as convience notation for: > >>>> ldr q8, .Lconstant > >>>> .Lconstant > >>>> .word 0x00000001 > >>>> .word 0x00000002 > >>>> .word 0x00000003 > >>>> .word 0x00000000 > >>>> > >>>> based on this comment in binutils' source [0]. I've asked for this > >>>> non-standard convience notation to be added to other assemblers [1], but > >>>> until then, we can remove it and get equivalent disassembly: > >>>> > >>> > >>> What do you mean by 'non-standard convenience notation'? Which asm > >>> 'standard' does Clang actually claim to implement? > >> > >> Well, for assembly 'standard' is a bit nebulous. But it's frustrating > >> when you can't find what the `=0x...` notation means in either the ARM > >> or GNU as manuals. The source of truth happened to be a comment in > >> the source [0] that explained that this was a "programmer friendly > >> notation." Sure, if you can find it. > >> > > > > Well, it is documented in the ARM manuals as the 'ldr pseudo > > instruction' for 32-bit ARM, and originally, it would only emit a > > literal if the value could not be loaded using a ordinary mov. > > FWIW It's certainly well-documented by common A64 assemblers too: > > http://infocenter.arm.com/help/topic/com.arm.doc.100069_0610_01_en/dom1395139540926.html > > https://sourceware.org/binutils/docs/as/AArch64-Opcodes.html#AArch64-Opcodes Thanks for those links, I've added them to the LLVM bug to show that this is documented behavior. -- Thanks, ~Nick Desaulniers ^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2018-08-21 18:14 UTC | newest] Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-08-20 22:40 [PATCH] arm64/crypto: remove non-standard notation Nick Desaulniers 2018-08-20 22:43 ` Nick Desaulniers 2018-08-21 0:04 ` Will Deacon 2018-08-21 12:23 ` Ard Biesheuvel 2018-08-21 16:50 ` Nick Desaulniers 2018-08-21 17:00 ` Ard Biesheuvel 2018-08-21 17:25 ` Robin Murphy 2018-08-21 18:13 ` Nick Desaulniers
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