Re: [PATCH v2] riscv: Handle zicsr/zifencei issue between gcc and binutils

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On 7/27/23 15:53, Conor Dooley wrote:
On Wed, Jul 26, 2023 at 08:41:55PM +0100, Conor Dooley wrote:
On Thu, Jul 27, 2023 at 03:34:16AM +0800, Mingzheng Xing wrote:
On 7/27/23 02:02, Conor Dooley wrote:
This is still broken for:
CONFIG_CLANG_VERSION=0
CONFIG_AS_IS_GNU=y
CONFIG_AS_VERSION=23500
CONFIG_LD_IS_BFD=y
CONFIG_LD_VERSION=23500
Do you mean that these CONFIG_* will cause kernel
compilation errors when paired with certain versions of GCC?
Or perhaps I misunderstood your meaning.
No, this section is generated by kconfig, although I messed up my
trimming of the list & accidentally removed the gcc version, rather
than the clang version. Here's the full thing:

CONFIG_CC_VERSION_TEXT="riscv64-unknown-linux-gnu-gcc (g2ee5e430018) 12.2.0"
CONFIG_CC_IS_GCC=y
CONFIG_GCC_VERSION=120200
CONFIG_CLANG_VERSION=0
CONFIG_AS_IS_GNU=y
CONFIG_AS_VERSION=23500
CONFIG_LD_IS_BFD=y
CONFIG_LD_VERSION=23500
CONFIG_LLD_VERSION=0
CONFIG_CC_CAN_LINK=y
CONFIG_CC_CAN_LINK_STATIC=y
CONFIG_CC_HAS_ASM_GOTO_OUTPUT=y
CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT=y
CONFIG_CC_HAS_ASM_INLINE=y
CONFIG_CC_HAS_NO_PROFILE_FN_ATTR=y
CONFIG_PAHOLE_VERSION=0
CONFIG_CONSTRUCTORS=y
CONFIG_IRQ_WORK=y
CONFIG_BUILDTIME_TABLE_SORT=y
I think this should sort things out for the even-older binutils case. I
took the opportunity to fix some grammatical issues that seem to have
snuck into the help text in your patch & to drop the \, since the
depends on fits in one line.

hi, Conor.

I reproduced the error with gcc-12.2.0 and binutils-2.35. I tried a
different solution, which I think makes the logic easier. Showing
the new patch code:

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 4c07b9189c86..a6fa1eed895c 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -569,25 +569,24 @@ config TOOLCHAIN_HAS_ZIHINTPAUSE

 config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
        def_bool y
-       # https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
-       depends on AS_IS_GNU && AS_VERSION >= 23800
+       depends on AS_IS_GNU && AS_VERSION >= 23600
        help
-         Newer binutils versions default to ISA spec version 20191213 which
-         moves some instructions from the I extension to the Zicsr and Zifencei
-         extensions.
+         Binutils has supported zicsr and zifencei extensions since version 2.36,
+         try to adapt to the changes by using explicit zicsr and zifencei via
+         -march. For two special cases, where clang<17 or gcc<11.1.0, we will
+         deal with them in CONFIG_TOOLCHAIN_NEEDS_OLD_ISA_SPEC.

 config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
        def_bool y
        depends on TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
        # https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e15bf8a16
-       depends on CC_IS_CLANG && CLANG_VERSION < 170000
-       help
-         Certain versions of clang do not support zicsr and zifencei via -march
-         but newer versions of binutils require it for the reasons noted in the
-         help text of CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI. This
-         option causes an older ISA spec compatible with these older versions
-         of clang to be passed to GAS, which has the same result as passing zicsr
-         and zifencei to -march.
+       # https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b03be74bad08c382da47e048007a78fa3fb4ef49
+       depends on (CC_IS_CLANG && CLANG_VERSION < 170000) || (CC_IS_GCC && GCC_VERSION < 110100)
+       help
+         Certain versions of clang and GCC do not support zicsr and zifencei via
+         -march. This option causes an older ISA spec compatible with these older
+         versions of clang and GCC to be passed to GAS, which has the same result
+         as passing zicsr and zifencei to -march.

 config FPU
        bool "FPU support"
diff --git a/arch/riscv/kernel/compat_vdso/Makefile b/arch/riscv/kernel/compat_vdso/Makefile
index 189345773e7e..b86e5e2c3aea 100644
--- a/arch/riscv/kernel/compat_vdso/Makefile
+++ b/arch/riscv/kernel/compat_vdso/Makefile
@@ -11,7 +11,13 @@ compat_vdso-syms += flush_icache
 COMPAT_CC := $(CC)
 COMPAT_LD := $(LD)

-COMPAT_CC_FLAGS := -march=rv32g -mabi=ilp32
+# binutils 2.35 does not support the zifencei extension, but in the ISA
+# spec 20191213, G stands for IMAFD_ZICSR_ZIFENCEI.
+ifdef CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
+       COMPAT_CC_FLAGS := -march=rv32g -mabi=ilp32
+else
+       COMPAT_CC_FLAGS := -march=rv32imafd -mabi=ilp32
+endif
 COMPAT_LD_FLAGS := -melf32lriscv

 # Disable attributes, as they're useless and break the build.
--
2.34.1


Here are the results of my tests:

gcc          binutils       patched         no patch(test on master)
11.4.0     2.35            ok                  ok
11.4.0     2.36            ok                  ok
11.4.0     2.38            ok                  ok

12.2.0     2.35            ok                  error[1]
12.2.0     2.36            ok                  error[2]
12.2.0     2.38            ok                  ok

10.5.0     2.35            ok                  ok
10.5.0     2.36            ok                  ok
10.5.0     2.38            ok                  error[3]

11.1.0     2.35            ok                  ok
11.1.0     2.36            ok                  ok
11.1.0     2.38            ok                  ok

11.2.0     2.35            ok                  ok
11.2.0     2.36            ok                  ok
11.2.0     2.38            ok                  ok

[1]
Assembler messages:
Fatal error: -march=rv32imafd_zicsr_zifencei: Invalid or unknown z ISA extension: 'zifencei'
make[2]: *** [arch/riscv/kernel/compat_vdso/Makefile:47: arch/riscv/kernel/compat_vdso/rt_sigreturn.o] Error 1

[2]
./arch/riscv/include/asm/vdso/gettimeofday.h: Assembler messages:
./arch/riscv/include/asm/vdso/gettimeofday.h:79: Error: unrecognized opcode `csrr a5,0xc01'
./arch/riscv/include/asm/vdso/gettimeofday.h:79: Error: unrecognized opcode `csrr a5,0xc01'
./arch/riscv/include/asm/vdso/gettimeofday.h:79: Error: unrecognized opcode `csrr a5,0xc01'
./arch/riscv/include/asm/vdso/gettimeofday.h:79: Error: unrecognized opcode `csrr a5,0xc01'
make[2]: *** [scripts/Makefile.build:243: arch/riscv/kernel/vdso/vgettimeofday.o] Error 1

[3]
cc1: error: '-march=rv64imac_zicsr_zifencei': unsupported ISA subset 'z'
cc1: error: ABI requires '-march=rv64'
make[2]: *** [scripts/Makefile.build:243: scripts/mod/empty.o] Error 1
make[2]: *** Waiting for unfinished jobs....
cc1: error: '-march=rv64imac_zicsr_zifencei': unsupported ISA subset 'z'
cc1: error: ABI requires '-march=rv64'

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e1b66ee88323..2d0d89213c97 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -571,25 +571,27 @@ config TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
  	def_bool y
  	# https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=aed44286efa8ae8717a77d94b51ac3614e2ca6dc
  	# https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98416dbb0a62579d4a7a4a76bab51b5b52fec2cd
-	depends on GCC_VERSION >= 120100 || (AS_IS_GNU && AS_VERSION >= 23800)
+	depends on AS_IS_GNU
+	depends on (GCC_VERSION >= 120100 && AS_VERSION >= 23600) || AS_VERSION >= 23800

Tests verified that explicit _ZICSR_ZIFENCEI via -march is required
for gcc>=12.1.0, but this only happens for binutils>=2.36,
binutils 2.35 + gcc>=12.1.0 does not need that. Considering
binutils 2.35 together complicates things. So what do you think
of the above new version patch?

Some more info:
- The commit[4] for patch changes.
- binutils 2.36 supports the zifencei extension[5] and splits
zifencei and zicsr from I[6].

[4] commit 0715372a06ce ("riscv: compat: vdso: Add COMPAT_VDSO base code implementation")
[5] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=5a1b31e1e1cee6e9f1c92abff59cdcfff0dddf30
[6] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=729a53530e86972d1143553a415db34e6e01d5d2

Thanks,
Mingzheng.

  	help
-	  Binutils-2.38 and GCC-12.1.0 bump default ISA spec to newer version
+	  Binutils-2.38 and GCC-12.1.0 bump the default ISA spec to version
  	  20191213 which moves some instructions from the I extension to the
-	  Zicsr and Zifencei extensions.
+	  Zicsr and Zifencei extensions. On the other hand, Binutils prior to
+	  2.35 does not understand these arguments and will error if they are
+	  passed.
config TOOLCHAIN_NEEDS_OLD_ISA_SPEC
  	def_bool y
  	depends on TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI
  	# https://github.com/llvm/llvm-project/commit/22e199e6afb1263c943c0c0d4498694e15bf8a16
  	# https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b03be74bad08c382da47e048007a78fa3fb4ef49
-	depends on (CC_IS_CLANG && CLANG_VERSION < 170000) || \
-		   (CC_IS_GCC && GCC_VERSION < 110100)
+	depends on (CC_IS_CLANG && CLANG_VERSION < 170000) || (CC_IS_GCC && GCC_VERSION < 110100)
  	help
-	  Certain versions of clang (or GCC) do not support zicsr and zifencei via
+	  Certain versions of clang and GCC do not support zicsr and zifencei via
  	  -march but newer versions of binutils require it for the reasons noted
  	  in the help text of CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI. This
  	  option causes an older ISA spec compatible with these older versions
-	  of clang (or GCC) to be passed to GAS, which has the same result as
+	  of clang and GCC to be passed to GAS, which has the same result as
  	  passing zicsr and zifencei to -march.
config FPU


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