[RFC,2/2] RISC-V: Attempt to enable TSO mode for TSO binaries

Message ID 20231127145603.2339644-3-christoph.muellner@vrull.eu
State New
Series RISC-V: Add dynamic TSO support |


Context Check Description
redhat-pt-bot/TryBot-apply_patch success Patch applied to master at the time it was sent
redhat-pt-bot/TryBot-32bit success Build for i686
linaro-tcwg-bot/tcwg_glibc_build--master-arm success Testing passed
linaro-tcwg-bot/tcwg_glibc_check--master-arm success Testing passed
linaro-tcwg-bot/tcwg_glibc_build--master-aarch64 success Testing passed
linaro-tcwg-bot/tcwg_glibc_check--master-aarch64 success Testing passed

Commit Message

Christoph Müllner Nov. 27, 2023, 2:56 p.m. UTC
  From: Christoph Müllner <christoph.muellner@vrull.eu>

The upcoming RISC-V Ssdtso specification introduces a bit in the senvcfg
CSR to switch the memory consistency model at run-time from RVWMO to TSO
(and back).  The active consistency model can therefore be switched on a
per-hart base and managed by the kernel on a per-process/thread base.

A RFC kernel patchset has been posted that provides a prctl API to get
and set the current consistency model.

This patch attempts to switch to the TSO consistency model in case
the ELF file requires a TSO machine and the machine does not run
in TSO mode.  If the attempt fails, we fall back to the old behaviour
and claim that the ELF file is not compatible with the host.

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>
 sysdeps/riscv/dl-machine.h | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)


diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
index ce537731dd..65be660a76 100644
--- a/sysdeps/riscv/dl-machine.h
+++ b/sysdeps/riscv/dl-machine.h
@@ -24,6 +24,7 @@ 
 #include <entry.h>
 #include <elf/elf.h>
 #include <sys/asm.h>
+#include <sys/prctl.h>
 #include <dl-tls.h>
 #include <dl-irel.h>
 #include <dl-static-tls.h>
@@ -72,9 +73,19 @@  elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
     return 0;
-  /* Execution of TSO binaries is not supported at this time.  */
+  /* Execution of TSO binaries depends on machine's consistency model.  */
   if (ehdr->e_flags & EF_RISCV_TSO)
-    return 0;
+    {
+      /* Attempt to get current consistency model.  */
+      int ret = prctl(PR_GET_MEMORY_CONSISTENCY_MODEL);
+      if (ret == -1)
+	return 0;
+      /* If we have a mismatch, let's try to switch to TSO.  */
+	return 0;
+    }
   return 1;