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Re: [Qemu-riscv] [Qemu-devel] [PATCH for 4.1] RISC-V: Ignore the S and U

From: Palmer Dabbelt
Subject: Re: [Qemu-riscv] [Qemu-devel] [PATCH for 4.1] RISC-V: Ignore the S and U extensions when formatting ISA strings
Date: Wed, 07 Aug 2019 10:25:14 -0700 (PDT)

On Wed, 07 Aug 2019 09:41:17 PDT (-0700), Peter Maydell wrote:
On Wed, 7 Aug 2019 at 16:02, Palmer Dabbelt <address@hidden> wrote:

The ISA strings we're providing from QEMU aren't actually legal RISC-V
ISA strings, as both the S and U extensions cannot exist as
single-letter extensions and must instead be multi-letter strings.
We're still using the ISA strings inside QEMU to track the availiable
extensions, so this patch just strips out the S and U extensions when
formatting ISA strings.

This boots Linux on top of 4.1-rc3, which no longer has the U extension
in /proc/cpuinfo.

Signed-off-by: Palmer Dabbelt <address@hidden>
This is another late one, but I'd like to target it for 4.1 as we're
providing illegal ISA strings and I don't want to bake that into a bunch
of other code.
 target/riscv/cpu.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index f8d07bd20ad7..4df14433d789 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -501,7 +501,22 @@ char *riscv_isa_string(RISCVCPU *cpu)
     char *p = isa_str + snprintf(isa_str, maxlen, "rv%d", TARGET_LONG_BITS);
     for (i = 0; i < sizeof(riscv_exts); i++) {
         if (cpu->env.misa & RV(riscv_exts[i])) {
-            *p++ = qemu_tolower(riscv_exts[i]);
+            char lower = qemu_tolower(riscv_exts[i]);
+            switch (lower) {
+            case 's':
+            case 'u':
+                /*
+                 * The 's' and 'u' extensions shouldn't be passed in the device
+                 * tree, but we still use them internally to track extension
+                 * sets.  Here we just explicitly remove them when formatting
+                 * an ISA string.
+                 */
+                break;
+            default:
+                *p++ = qemu_tolower(riscv_exts[i]);

 *p++ = lower;  ?

Yes, thanks -- that's why I pulled the variable out in the first place :)

-- PMM

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