| Message ID | 20210702023010.53289-1-kito.cheng@sifive.com |
|---|---|
| State | New |
| Headers | show |
| Series | docs: Add 'S' to Machine Constraints for RISC-V | expand |
On 2021-07-02, Kito Cheng wrote: >It was undocument before, but already used in linux kernel, so LLVM >community suggest we should document that, so that make it become >supported/documented/non-internal machine constraints. > >gcc/ChangeLog: > > PR target/101275 > * doc/md.text (Machine Constraints): Document the 'S' constraints > for RISC-V. >--- > gcc/doc/md.texi | 3 +++ > 1 file changed, 3 insertions(+) > >diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi >index 00caf3844cc..b776623e8a5 100644 >--- a/gcc/doc/md.texi >+++ b/gcc/doc/md.texi >@@ -3536,6 +3536,9 @@ A 5-bit unsigned immediate for CSR access instructions. > @item A > An address that is held in a general-purpose register. > >+@item S >+A constant call address. >+ > @end table > > @item RX---@file{config/rx/constraints.md} >-- >2.31.1 > Thanks for the patch! To clarify, 'S' is used by the aarch64 port of the Linux kernel. (https://github.com/ClangBuiltLinux/linux/issues/13) It was proposed as one way to make __vdso_rt_sigreturn in arch/riscv/kernel/signal.c less hacky but we have agreed that riscv should just use the existing mechanism (e.g. arch/arm64/kernel/vdso/gen_vdso_offsets.sh) as used by a few other ports. That said, 'S' is still useful as it enables flexible modifiers (e.g. `%got_pcrel_hi, %pcrel_hi`) in inline asm.
On 2021-07-02, Kito Cheng wrote: >It was undocument before, but already used in linux kernel, so LLVM >community suggest we should document that, so that make it become >supported/documented/non-internal machine constraints. > >gcc/ChangeLog: > > PR target/101275 > * doc/md.text (Machine Constraints): Document the 'S' constraints > for RISC-V. >--- > gcc/doc/md.texi | 3 +++ > 1 file changed, 3 insertions(+) > >diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi >index 00caf3844cc..b776623e8a5 100644 >--- a/gcc/doc/md.texi >+++ b/gcc/doc/md.texi >@@ -3536,6 +3536,9 @@ A 5-bit unsigned immediate for CSR access instructions. > @item A > An address that is held in a general-purpose register. > >+@item S >+A constant call address. >+ > @end table > > @item RX---@file{config/rx/constraints.md} >-- >2.31.1 > Ping on this:) 'S' can be used on either a variable or a function. Does "A constant call address." need change?
On Wed, 07 Jul 2021 16:26:25 PDT (-0700), i@maskray.me wrote: > On 2021-07-02, Kito Cheng wrote: >>It was undocument before, but already used in linux kernel, so LLVM >>community suggest we should document that, so that make it become >>supported/documented/non-internal machine constraints. >> >>gcc/ChangeLog: >> >> PR target/101275 >> * doc/md.text (Machine Constraints): Document the 'S' constraints >> for RISC-V. >>--- >> gcc/doc/md.texi | 3 +++ >> 1 file changed, 3 insertions(+) >> >>diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi >>index 00caf3844cc..b776623e8a5 100644 >>--- a/gcc/doc/md.texi >>+++ b/gcc/doc/md.texi >>@@ -3536,6 +3536,9 @@ A 5-bit unsigned immediate for CSR access instructions. >> @item A >> An address that is held in a general-purpose register. >> >>+@item S >>+A constant call address. >>+ >> @end table >> >> @item RX---@file{config/rx/constraints.md} >>-- >>2.31.1 >> > > Ping on this:) Thanks, I hadn't had time to look a this but it was on the list. > 'S' can be used on either a variable or a function. Does "A constant call address." need change? I think so: this can certainly be used to generate arbitrary constant addresses into assembly, but I don't remember if there was some reason it was listed as only applying to call addresses. It certainly could just be a historical artifact, as those strings tend to bit rot when they're internal, but I wanted to at least take a look. Also: IIUC we're supposed to remove the @internal when something is documented (though I remember having said that before, so I might be mistaken).
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi index 00caf3844cc..b776623e8a5 100644 --- a/gcc/doc/md.texi +++ b/gcc/doc/md.texi @@ -3536,6 +3536,9 @@ A 5-bit unsigned immediate for CSR access instructions. @item A An address that is held in a general-purpose register. +@item S +A constant call address. + @end table @item RX---@file{config/rx/constraints.md}