runtime: consolidate function descriptor definitions on PPC64

This reapplies CL 481075, which was a reappliation of CL 478917.

This CL has been reverted twice now due to conflicts with CL 392854 /
CL 481061, which had bugs and had to be reverted.

Now this CL skips the conflicting changes to runtime/cgo/asm_ppc64x.s,
which will be merged directly into a new version of CL 392854 /
CL 481061. That way, if there are _more_ issues, this CL need not be
involved in any more reverts.

Change-Id: I2801b918faf9418dd0edff19f2a63f4d9e08896c
Reviewed-on: https://go-review.googlesource.com/c/go/+/485335
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Michael Pratt <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

src/runtime/asm_ppc64x.h

@@ -24,16 +24,32 @@
 
 #define FIXED_FRAME 32
 
-// aix/ppc64 uses XCOFF which has function descriptors.
+// aix/ppc64 uses XCOFF which uses function descriptors.
+// AIX cannot perform the TOC relocation in a text section.
+// Therefore, these descriptors must live in a data section.
 #ifdef GOOS_aix
 #ifdef GOARCH_ppc64
 #define GO_PPC64X_HAS_FUNCDESC
+#define DEFINE_PPC64X_FUNCDESC(funcname, localfuncname)	\
+	DATA	funcname+0(SB)/8, $localfuncname(SB) 	\
+	DATA	funcname+8(SB)/8, $TOC(SB)		\
+	DATA	funcname+16(SB)/8, $0			\
+	GLOBL	funcname(SB), NOPTR, $24
 #endif
 #endif
 
-// linux/ppc64 uses ELFv1 which has function descriptors.
+// linux/ppc64 uses ELFv1 which uses function descriptors.
+// These must also look like ABI0 functions on linux/ppc64
+// to work with abi.FuncPCABI0(sigtramp) in os_linux.go.
+// Only static codegen is supported on linux/ppc64, so TOC
+// is not needed.
 #ifdef GOOS_linux
 #ifdef GOARCH_ppc64
 #define GO_PPC64X_HAS_FUNCDESC
+#define DEFINE_PPC64X_FUNCDESC(funcname, localfuncname)	\
+	TEXT	funcname(SB),NOSPLIT|NOFRAME,$0		\
+		DWORD	$localfuncname(SB)		\
+		DWORD	$0				\
+		DWORD	$0
 #endif
 #endif

src/runtime/asm_ppc64x.s

@@ -744,26 +744,11 @@ TEXT runtime·setg(SB), NOSPLIT, $0-8
 	BL	runtime·save_g(SB)
 	RET
 
-#ifdef GOARCH_ppc64
-#ifdef GOOS_aix
-DATA    setg_gcc<>+0(SB)/8, $_setg_gcc<>(SB)
-DATA    setg_gcc<>+8(SB)/8, $TOC(SB)
-DATA    setg_gcc<>+16(SB)/8, $0
-GLOBL   setg_gcc<>(SB), NOPTR, $24
+#ifdef GO_PPC64X_HAS_FUNCDESC
+DEFINE_PPC64X_FUNCDESC(setg_gcc<>, _setg_gcc<>)
+TEXT _setg_gcc<>(SB),NOSPLIT|NOFRAME,$0-0
 #else
 TEXT setg_gcc<>(SB),NOSPLIT|NOFRAME,$0-0
-	DWORD	$_setg_gcc<>(SB)
-	DWORD	$0
-	DWORD	$0
-#endif
-#endif
-
-// void setg_gcc(G*); set g in C TLS.
-// Must obey the gcc calling convention.
-#ifdef GOARCH_ppc64le
-TEXT setg_gcc<>(SB),NOSPLIT|NOFRAME,$0-0
-#else
-TEXT _setg_gcc<>(SB),NOSPLIT|NOFRAME,$0-0
 #endif
 	// The standard prologue clobbers R31, which is callee-save in
 	// the C ABI, so we have to use $-8-0 and save LR ourselves.

src/runtime/rt0_aix_ppc64.s

@@ -3,13 +3,11 @@
 // license that can be found in the LICENSE file.
 
 #include "textflag.h"
+#include "asm_ppc64x.h"
 
 // _rt0_ppc64_aix is a function descriptor of the entrypoint function
 // __start. This name is needed by cmd/link.
-DATA	_rt0_ppc64_aix+0(SB)/8, $__start<>(SB)
-DATA	_rt0_ppc64_aix+8(SB)/8, $TOC(SB)
-GLOBL	_rt0_ppc64_aix(SB), NOPTR, $16
-
+DEFINE_PPC64X_FUNCDESC(_rt0_ppc64_aix, __start<>)
 
 // The starting function must return in the loader to
 // initialise some libraries, especially libthread which
@@ -37,11 +35,7 @@ TEXT __start<>(SB),NOSPLIT,$-8
 	BL _main(SB)
 
 
-DATA	main+0(SB)/8, $_main(SB)
-DATA	main+8(SB)/8, $TOC(SB)
-DATA	main+16(SB)/8, $0
-GLOBL	main(SB), NOPTR, $24
-
+DEFINE_PPC64X_FUNCDESC(main, _main)
 TEXT _main(SB),NOSPLIT,$-8
 	MOVD $runtime·rt0_go(SB), R12
 	MOVD R12, CTR
@@ -181,10 +175,7 @@ done:
 	MOVD	R0, LR
 	RET
 
-DATA	_rt0_ppc64_aix_lib_go+0(SB)/8, $__rt0_ppc64_aix_lib_go(SB)
-DATA	_rt0_ppc64_aix_lib_go+8(SB)/8, $TOC(SB)
-DATA	_rt0_ppc64_aix_lib_go+16(SB)/8, $0
-GLOBL	_rt0_ppc64_aix_lib_go(SB), NOPTR, $24
+DEFINE_PPC64X_FUNCDESC(_rt0_ppc64_aix_lib_go, __rt0_ppc64_aix_lib_go)
 
 TEXT __rt0_ppc64_aix_lib_go(SB),NOSPLIT,$0
 	MOVD	_rt0_ppc64_aix_lib_argc<>(SB), R3

src/runtime/rt0_linux_ppc64.s

@@ -3,17 +3,10 @@
 // license that can be found in the LICENSE file.
 
 #include "textflag.h"
+#include "asm_ppc64x.h"
 
-// actually a function descriptor for _main<>(SB)
-TEXT _rt0_ppc64_linux(SB),NOSPLIT,$0
-	DWORD $_main<>(SB)
-	DWORD $0
-	DWORD $0
-
-TEXT main(SB),NOSPLIT,$0
-	DWORD $_main<>(SB)
-	DWORD $0
-	DWORD $0
+DEFINE_PPC64X_FUNCDESC(_rt0_ppc64_linux, _main<>)
+DEFINE_PPC64X_FUNCDESC(main, _main<>)
 
 TEXT _main<>(SB),NOSPLIT,$-8
 	// In a statically linked binary, the stack contains argc,

src/runtime/sys_linux_ppc64x.s

@@ -447,7 +447,12 @@ TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
 	MOVD	24(R1), R2
 	RET
 
-#ifdef GOARCH_ppc64le
+#ifdef GO_PPC64X_HAS_FUNCDESC
+DEFINE_PPC64X_FUNCDESC(runtime·sigtramp, sigtramp<>)
+// cgo isn't supported on ppc64, but we need to supply a cgoSigTramp function.
+DEFINE_PPC64X_FUNCDESC(runtime·cgoSigtramp, sigtramp<>)
+TEXT sigtramp<>(SB),NOSPLIT|NOFRAME|TOPFRAME,$0
+#else
 // ppc64le doesn't need function descriptors
 // Save callee-save registers in the case of signal forwarding.
 // Same as on ARM64 https://golang.org/issue/31827 .
@@ -456,13 +461,6 @@ TEXT runtime·sigfwd(SB),NOSPLIT,$0-32
 // a function pointer) as R2 may not be preserved when calling this
 // function. In those cases, the caller preserves their R2.
 TEXT runtime·sigtramp(SB),NOSPLIT|NOFRAME,$0
-#else
-// function descriptor for the real sigtramp
-TEXT runtime·sigtramp(SB),NOSPLIT|NOFRAME,$0
-	DWORD	$sigtramp<>(SB)
-	DWORD	$0
-	DWORD	$0
-TEXT sigtramp<>(SB),NOSPLIT|NOFRAME|TOPFRAME,$0
 #endif
 	// This is called with ELF calling conventions. Convert to Go.
 	// Allocate space for argument storage to call runtime.sigtrampgo.
@@ -491,7 +489,6 @@ TEXT sigtramp<>(SB),NOSPLIT|NOFRAME|TOPFRAME,$0
 	RET
 
 #ifdef GOARCH_ppc64le
-// ppc64le doesn't need function descriptors
 TEXT runtime·cgoSigtramp(SB),NOSPLIT|NOFRAME,$0
 	// The stack unwinder, presumably written in C, may not be able to
 	// handle Go frame correctly. So, this function is NOFRAME, and we
@@ -586,14 +583,6 @@ sigtrampnog:
 	MOVD	R12, CTR
 	MOVD	R10, LR // restore LR
 	JMP	(CTR)
-#else
-// function descriptor for the real sigtramp
-TEXT runtime·cgoSigtramp(SB),NOSPLIT|NOFRAME,$0
-	DWORD	$cgoSigtramp<>(SB)
-	DWORD	$0
-	DWORD	$0
-TEXT cgoSigtramp<>(SB),NOSPLIT,$0
-	JMP	sigtramp<>(SB)
 #endif
 
 // Used by cgoSigtramp to inspect without clobbering R30/R31 via runtime.load_g.