[XS] Change in coreboot[main]: libpayload/x86: Add x86-64 support to rdtsc()

[Subrata Banik (Code Review)]

Subrata Banik has submitted this change. ( https://review.coreboot.org/c/coreboot/+/83414?usp=email )

Change subject: libpayload/x86: Add x86-64 support to rdtsc()
......................................................................

libpayload/x86: Add x86-64 support to rdtsc()

This patch adds support for x86-64 to the rdtsc() function, allowing
it to correctly read the Time Stamp Counter (TSC) on both 32-bit and
64-bit x86 architectures.

BUG=b:242829490, b:351851626
TEST=Builds and boots on google/rex0 and google/rex64 systems and
manually verified correct TSC readings on x86-32 and x86-64 hardware.

Change-Id: I0afac3db2e82a245a37c2e5cf2302bf1dad62c01
Signed-off-by: Subrata Banik 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83414
Tested-by: build bot (Jenkins) 
Reviewed-by: Julius Werner 
---
M payloads/libpayload/include/x86/arch/rdtsc.h
1 file changed, 3 insertions(+), 3 deletions(-)

Approvals:
  Julius Werner: Looks good to me, approved
  build bot (Jenkins): Verified

diff --git a/payloads/libpayload/include/x86/arch/rdtsc.h b/payloads/libpayload/include/x86/arch/rdtsc.h
index 41ab24a..2c92a9f 100644
--- a/payloads/libpayload/include/x86/arch/rdtsc.h
+++ b/payloads/libpayload/include/x86/arch/rdtsc.h
@@ -33,9 +33,9 @@

static u64 rdtsc(void)
 {
-	u64 val;
-	__asm__ __volatile__ ("rdtsc" : "=A" (val));
-	return val;
+	u32 lo, hi;
+	__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
+	return (u64)hi << 32 | lo;
 }

#endif