selftests: vDSO: fix the way vDSO functions are called for powerpc

vdso_test_correctness test fails on powerpc:

~ # ./vdso_test_correctness
...
[RUN] Testing clock_gettime for clock CLOCK_REALTIME_ALARM (8)...
[FAIL] No such clock, but __vdso_clock_gettime returned 22
[RUN] Testing clock_gettime for clock CLOCK_BOOTTIME_ALARM (9)...
[FAIL] No such clock, but __vdso_clock_gettime returned 22
[RUN] Testing clock_gettime for clock CLOCK_SGI_CYCLE (10)...
[FAIL] No such clock, but __vdso_clock_gettime returned 22
...
[RUN] Testing clock_gettime for clock invalid (-1)...
[FAIL] No such clock, but __vdso_clock_gettime returned 22
[RUN] Testing clock_gettime for clock invalid (-2147483648)...
[FAIL] No such clock, but __vdso_clock_gettime returned 22
[RUN] Testing clock_gettime for clock invalid (2147483647)...
[FAIL] No such clock, but __vdso_clock_gettime returned 22

On powerpc, a call to a VDSO function is not an ordinary C function
call. Unlike several architectures which returns a negative error code
in case of an error, powerpc sets CR[SO] and returns the error code
as a positive value.

Define and use a macro called VDSO_CALL() which takes a pointer
to the function to call, the number of arguments and the arguments.

Also update ABI vdso documentation to reflect this subtlety.

Provide a specific version of VDSO_CALL() for powerpc that negates
the error code on return when CR[SO] is set.

Fixes: c7e5789b24d3 ("kselftest: Move test_vdso to the vDSO test suite")
Fixes: 2e9a97256616 ("selftests: vdso: Add a selftest for vDSO getcpu()")
Fixes: 693f5ca08ca0 ("kselftest: Extend vDSO selftest")
Fixes: b2f1c3db2887 ("kselftest: Extend vdso correctness test to clock_gettime64")
Fixes: 4920a2590e91 ("selftests/vDSO: add tests for vgetrandom")
Signed-off-by: Christophe Leroy <[e-mail]>
Acked-by: Shuah Khan <[e-mail]>
Signed-off-by: Jason A. Donenfeld <[e-mail]>

Documentation/ABI/stable/vdso

···
 the vDSO and it often contains useful and highly-optimized alternatives
 to real syscalls.
 
-These functions are called just like ordinary C function according to
-your platform's ABI.  Call them from a sensible context.  (For example,
-if you set CS on x86 to something strange, the vDSO functions are
+These functions are called according to your platform's ABI. On many
+platforms they are called just like ordinary C function. On other platforms
+(ex: powerpc) they are called with the same convention as system calls which
+is different from ordinary C functions. Call them from a sensible context.
+(For example, if you set CS on x86 to something strange, the vDSO functions are
 within their rights to crash.)  In addition, if you pass a bad
 pointer to a vDSO function, you might get SIGSEGV instead of -EFAULT.
 

tools/testing/selftests/vDSO/vdso_call.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Macro to call vDSO functions
+ *
+ * Copyright (C) 2024 Christophe Leroy <[e-mail]>, CS GROUP France
+ */
+#ifndef __VDSO_CALL_H__
+#define __VDSO_CALL_H__
+
+#ifdef __powerpc__
+
+#define LOADARGS_1(fn, __arg1) do {					\
+	_r0 = fn;							\
+	_r3 = (long)__arg1;						\
+} while (0)
+
+#define LOADARGS_2(fn, __arg1, __arg2) do {				\
+	_r0 = fn;							\
+	_r3 = (long)__arg1;						\
+	_r4 = (long)__arg2;						\
+} while (0)
+
+#define LOADARGS_3(fn, __arg1, __arg2, __arg3) do {			\
+	_r0 = fn;							\
+	_r3 = (long)__arg1;						\
+	_r4 = (long)__arg2;						\
+	_r5 = (long)__arg3;						\
+} while (0)
+
+#define LOADARGS_5(fn, __arg1, __arg2, __arg3, __arg4, __arg5) do {	\
+	_r0 = fn;							\
+	_r3 = (long)__arg1;						\
+	_r4 = (long)__arg2;						\
+	_r5 = (long)__arg3;						\
+	_r6 = (long)__arg4;						\
+	_r7 = (long)__arg5;						\
+} while (0)
+
+#define VDSO_CALL(fn, nr, args...) ({					\
+	register void *_r0 asm ("r0");					\
+	register long _r3 asm ("r3");					\
+	register long _r4 asm ("r4");					\
+	register long _r5 asm ("r5");					\
+	register long _r6 asm ("r6");					\
+	register long _r7 asm ("r7");					\
+	register long _r8 asm ("r8");					\
+	register long _rval asm ("r3");					\
+									\
+	LOADARGS_##nr(fn, args);					\
+									\
+	asm volatile(							\
+		"	mtctr %0\n"					\
+		"	bctrl\n"					\
+		"	bns+	1f\n"					\
+		"	neg	3, 3\n"					\
+		"1:"							\
+		: "+r" (_r0), "=r" (_r3), "+r" (_r4), "+r" (_r5),	\
+		  "+r" (_r6), "+r" (_r7), "+r" (_r8)			\
+		: "r" (_rval)						\
+		: "r9", "r10", "r11", "r12", "cr0", "cr1", "cr5",	\
+		  "cr6", "cr7", "xer", "lr", "ctr", "memory"		\
+	);								\
+	_rval;								\
+})
+
+#else
+#define VDSO_CALL(fn, nr, args...)	fn(args)
+#endif
+
+#endif

tools/testing/selftests/vDSO/vdso_test_abi.c

···
 
 #include "../kselftest.h"
 #include "vdso_config.h"
+#include "vdso_call.h"
 
 extern void *vdso_sym(const char *version, const char *name);
 extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
···
 	}
 
 	struct timeval tv;
-	long ret = vdso_gettimeofday(&tv, 0);
+	long ret = VDSO_CALL(vdso_gettimeofday, 2, &tv, 0);
 
 	if (ret == 0) {
 		ksft_print_msg("The time is %lld.%06lld\n",
···
 	}
 
 	struct timespec ts;
-	long ret = vdso_clock_gettime(clk_id, &ts);
+	long ret = VDSO_CALL(vdso_clock_gettime, 2, clk_id, &ts);
 
 	if (ret == 0) {
 		ksft_print_msg("The time is %lld.%06lld\n",
···
 		return;
 	}
 
-	long ret = vdso_time(NULL);
+	long ret = VDSO_CALL(vdso_time, 1, NULL);
 
 	if (ret > 0) {
 		ksft_print_msg("The time in hours since January 1, 1970 is %lld\n",
···
 	}
 
 	struct timespec ts, sys_ts;
-	long ret = vdso_clock_getres(clk_id, &ts);
+	long ret = VDSO_CALL(vdso_clock_getres, 2, clk_id, &ts);
 
 	if (ret == 0) {
 		ksft_print_msg("The vdso resolution is %lld %lld\n",

tools/testing/selftests/vDSO/vdso_test_correctness.c

···
 #include <limits.h>
 
 #include "vdso_config.h"
+#include "vdso_call.h"
 #include "../kselftest.h"
 
 static const char **name;
···
 
 		ret_sys = sys_getcpu(&cpu_sys, &node_sys, 0);
 		if (vdso_getcpu)
-			ret_vdso = vdso_getcpu(&cpu_vdso, &node_vdso, 0);
+			ret_vdso = VDSO_CALL(vdso_getcpu, 3, &cpu_vdso, &node_vdso, 0);
 		if (vgetcpu)
 			ret_vsys = vgetcpu(&cpu_vsys, &node_vsys, 0);
 
···
 
 	if (sys_clock_gettime(clock, &start) < 0) {
 		if (errno == EINVAL) {
-			vdso_ret = vdso_clock_gettime(clock, &vdso);
+			vdso_ret = VDSO_CALL(vdso_clock_gettime, 2, clock, &vdso);
 			if (vdso_ret == -EINVAL) {
 				printf("[OK]\tNo such clock.\n");
 			} else {
···
 		return;
 	}
 
-	vdso_ret = vdso_clock_gettime(clock, &vdso);
+	vdso_ret = VDSO_CALL(vdso_clock_gettime, 2, clock, &vdso);
 	end_ret = sys_clock_gettime(clock, &end);
 
 	if (vdso_ret != 0 || end_ret != 0) {
···
 
 	if (sys_clock_gettime64(clock, &start) < 0) {
 		if (errno == EINVAL) {
-			vdso_ret = vdso_clock_gettime64(clock, &vdso);
+			vdso_ret = VDSO_CALL(vdso_clock_gettime64, 2, clock, &vdso);
 			if (vdso_ret == -EINVAL) {
 				printf("[OK]\tNo such clock.\n");
 			} else {
···
 		return;
 	}
 
-	vdso_ret = vdso_clock_gettime64(clock, &vdso);
+	vdso_ret = VDSO_CALL(vdso_clock_gettime64, 2, clock, &vdso);
 	end_ret = sys_clock_gettime64(clock, &end);
 
 	if (vdso_ret != 0 || end_ret != 0) {
···
 		return;
 	}
 
-	vdso_ret = vdso_gettimeofday(&vdso, &vdso_tz);
+	vdso_ret = VDSO_CALL(vdso_gettimeofday, 2, &vdso, &vdso_tz);
 	end_ret = sys_gettimeofday(&end, NULL);
 
 	if (vdso_ret != 0 || end_ret != 0) {
···
 	}
 
 	/* And make sure that passing NULL for tz doesn't crash. */
-	vdso_gettimeofday(&vdso, NULL);
+	VDSO_CALL(vdso_gettimeofday, 2, &vdso, NULL);
 }
 
 int main(int argc, char **argv)

tools/testing/selftests/vDSO/vdso_test_getcpu.c

···
 #include "../kselftest.h"
 #include "parse_vdso.h"
 #include "vdso_config.h"
+#include "vdso_call.h"
 
 struct getcpu_cache;
 typedef long (*getcpu_t)(unsigned int *, unsigned int *,
···
 		return KSFT_SKIP;
 	}
 
-	ret = get_cpu(&cpu, &node, 0);
+	ret = VDSO_CALL(get_cpu, 3, &cpu, &node, 0);
 	if (ret == 0) {
 		printf("Running on CPU %u node %u\n", cpu, node);
 	} else {

tools/testing/selftests/vDSO/vdso_test_getrandom.c

···
 #include "../kselftest.h"
 #include "parse_vdso.h"
 #include "vdso_config.h"
+#include "vdso_call.h"
 
 #ifndef timespecsub
 #define	timespecsub(tsp, usp, vsp)					\
···
 		printf("%s is missing!\n", name);
 		exit(KSFT_FAIL);
 	}
-	ret = vgrnd.fn(NULL, 0, 0, &vgrnd.params, ~0UL);
+	ret = VDSO_CALL(vgrnd.fn, 5, NULL, 0, 0, &vgrnd.params, ~0UL);
 	if (ret == -ENOSYS) {
 		printf("unsupported architecture\n");
 		exit(KSFT_SKIP);
···
 			exit(KSFT_FAIL);
 		}
 	}
-	return vgrnd.fn(buf, len, flags, state, vgrnd.params.size_of_opaque_state);
+	return VDSO_CALL(vgrnd.fn, 5, buf, len, flags, state, vgrnd.params.size_of_opaque_state);
 }
 
 enum { TRIALS = 25000000, THREADS = 256 };

tools/testing/selftests/vDSO/vdso_test_gettimeofday.c

···
 #include "../kselftest.h"
 #include "parse_vdso.h"
 #include "vdso_config.h"
+#include "vdso_call.h"
 
 int main(int argc, char **argv)
 {
···
 	}
 
 	struct timeval tv;
-	long ret = gtod(&tv, 0);
+	long ret = VDSO_CALL(gtod, 2, &tv, 0);
 
 	if (ret == 0) {
 		printf("The time is %lld.%06lld\n",