Merge pull request #313 from dkg/test-variadic-promotion

Test variadic promotion

.gitignore

@@ -8,6 +8,7 @@ test/run_*
 test/repeat_random
 test/getentropy_test
 test/syscall_test
+test/variadic_promotion
 
 src/libfaketime.dylib.1
 src/libfaketime.1.dylib

src/Makefile

@@ -48,6 +48,11 @@
 #         - (On GNU/Linux only) intercept glibc's syscall() for known relevant syscalls.
 #           If enabled, this currently only works to divert the getrandom syscall.
 #
+#         - note that on unusual architectures, if INTERCEPT_SYSCALL is set, you may
+#           need to explicitly define variadic_promotion_t (e.g. by putting
+#           -Dvariadic_promotion_t=int into CFLAGS).  See src/faketime_common.h for
+#           more info.
+#
 #     FORCE_MONOTONIC_FIX
 #         - If the test program hangs forever on
 #                  " pthread_cond_timedwait: CLOCK_MONOTONIC test

src/faketime_common.h

@@ -58,4 +58,43 @@ struct ft_shared_s
 #include <mach/mach_port.h>
 #endif
 
+/*
+   Variadic Argument Re-packing
+
+   Functions with variadic arguments typically have most arguments
+   passed on the stack, but it varies across ABIs.
+
+   C specifies that variadic arguments that are smaller than some
+   standard promotion size are promoted to "int or larger".  If your
+   platform's ABI only promotes to "int" and not "long" (and "int" and
+   "long" differ on your platform), you should probably add
+   -Dvariadic_promotion_t=int to CFLAGS.
+
+   Note that some ABIs do not put all the variadic arguments on the
+   stack.  For example, x86-64 puts float and double variadic
+   arguments into floating point registers, according to
+   https://www.uclibc.org/docs/psABI-x86_64.pdf
+
+   The only variadic function faketime cares about intercepting is
+   syscall.  But we don't believe that any syscalls expect float or
+   double arguments, so we hope all the rest will be on the stack.
+   tests/variadic/ attempts to confirm this if you are compiling
+   with -DINTERCEPT_SYSCALL.
+
+   If libc were capable of exposing a variadic form of syscall, we
+   could depend on that and drop this approach, which would be
+   preferable: https://sourceware.org/bugzilla/show_bug.cgi?id=27508
+*/
+#ifndef variadic_promotion_t
+#define variadic_promotion_t long
+#endif
+
+/*
+   The Linux kernel appears to have baked-in 6 as the maximum number
+   of arguments for a syscall beyond the syscall number itself.
+*/
+#ifndef syscall_max_args
+#define syscall_max_args 6
+#endif
+
 #endif

src/libfaketime.c

@@ -3781,23 +3781,9 @@ long syscall(long number, ...) {
     return clock_gettime(clk_id, tp);
   }
 
-/*
-   Invocations of C variadic arguments that are smaller than int are
-   promoted to int.  For larger arguments, it's likely that they are
-   chopped into int-sized pieces.
-
-   So the passthrough part of this code is attempting to reverse that
-   ABI so we can pass the arguments back into syscall().
-
-   Note that the Linux kernel appears to have baked-in 6 as the
-   maximum number of arguments for a syscall beyond the syscall number
-   itself.
-*/
-#define vararg_promotion_t long
-#define syscall_max_args 6
-  vararg_promotion_t a[syscall_max_args];
+  variadic_promotion_t a[syscall_max_args];
   for (int i = 0; i < syscall_max_args; i++)
-    a[i] = va_arg(ap, vararg_promotion_t);
+    a[i] = va_arg(ap, variadic_promotion_t);
   va_end(ap);
   if (!initialized)
     ftpl_init();

test/Makefile

@@ -1,7 +1,7 @@
 CC = gcc
 
-CFLAGS = -std=gnu99 -Wall -DFAKE_STAT -Werror -Wextra $(FAKETIME_COMPILE_CFLAGS)
-LDFLAGS = -lrt -lpthread
+CFLAGS += -std=gnu99 -Wall -DFAKE_STAT -Werror -Wextra $(FAKETIME_COMPILE_CFLAGS)
+LDFLAGS += -lrt -lpthread
 
 SRC = timetest.c
 OBJ = ${SRC:.c=.o}
@@ -9,7 +9,13 @@ OBJ = ${SRC:.c=.o}
 TEST_SNIPPETS = $(notdir $(basename $(wildcard snippets/*.c)))
 EXPECTATIONS= $(notdir $(basename $(wildcard snippets/*.variable)))
 
-all: timetest test
+ALL_TESTS = timetest test
+
+ifneq ($(filter -DINTERCEPT_SYSCALL,${CFLAGS}),)
+ALL_TESTS += confirm_variadic_promotion
+endif
+
+all: $(ALL_TESTS)
 
 .c.o:
 	${CC} -c ${CFLAGS} $<
@@ -31,6 +37,13 @@ functest:
 randomtest: repeat_random
 	./randomtest.sh
 
+# ensure our variadic argument unpacking/repacking works as expected
+confirm_variadic_promotion: variadic_promotion
+	./variadic_promotion
+variadic_promotion: variadic/main.o variadic/outer.o variadic/inner.o
+	${CC} -o $@ ${CFLAGS} $^
+variadic/%.o: variadic/%.c
+	${CC} -c -o $@ ${CFLAGS} $<
 
 # run snippet tests
 snippets: test_variable_data test_library_constructors
@@ -57,7 +70,7 @@ use_lib_%: _use_lib_test.c snippets/%.c lib%.so
 ## cleanup and metainformation
 
 clean:
-	@rm -f ${OBJ} timetest getrandom_test syscall_test $(foreach f,${TEST_SNIPPETS},use_lib_${f} lib${f}.so run_${f})
+	@rm -f ${OBJ} timetest getrandom_test syscall_test $(foreach f,${TEST_SNIPPETS},use_lib_${f} lib${f}.so run_${f}) variadic_promotion variadic/*.o
 
 distclean: clean
 	@echo

test/variadic/inner.c

@@ -0,0 +1,46 @@
+
+#include <stdio.h>
+#include <wchar.h>
+#include <stdarg.h>
+#include <stddef.h>
+
+/*   round 0:  c, s, wc, i, wi */
+long inner0(char *out, ...) {
+  char c = 0;
+  short s = 0;
+  wchar_t wc = 0;
+  int i = 0;
+  wint_t wi = 0;
+
+  va_list ap;
+  va_start(ap, out);
+  c = va_arg(ap, int);
+  s = va_arg(ap, int);
+  wc = va_arg(ap, typeof(wc));
+  i = va_arg(ap, typeof(i));
+  wi = va_arg(ap, typeof(wi));
+  va_end(ap);
+
+  int ret = sprintf(out, "c: 0x%x s: 0x%x wc: 0x%lx i: 0x%x wi: 0x%x\n", c, s, (long)wc, i, wi);
+  return ret;
+}
+/*   round 1: l, ll, ptr, pd, sz */
+long inner1(char *out, ...) {
+  long l = 0;
+  long long ll = 0;
+  void *ptr = NULL;
+  ptrdiff_t pd = 0;
+  size_t sz = 0;
+
+  va_list ap;
+  va_start(ap, out);
+  l = va_arg(ap, typeof(l));
+  ll = va_arg(ap, typeof(ll));
+  ptr = va_arg(ap, typeof(ptr));
+  pd = va_arg(ap, typeof(pd));
+  sz = va_arg(ap, typeof(sz));
+  va_end(ap);
+
+  int ret = sprintf(out, "l: 0x%lx ll: 0x%llx ptr: %p pd: 0x%tx sz: 0x%zx\n", l, ll, ptr, pd, sz);
+  return ret;
+}

test/variadic/main.c

@@ -0,0 +1,70 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stddef.h>
+#include <wchar.h>
+
+extern long outer(long num, char *out, ...);
+extern long inner0(char *out, ...);
+extern long inner1(char *out, ...);
+
+#define bufsize 2048
+
+static int compare_buffers(int round,
+                            long ret_outer, long ret_inner,
+                            const char* outer, const char* inner) {
+  int ret = 0;
+  if (ret_outer != ret_inner) {
+    printf("Round %d: return values differ (outer: %ld inner: %ld)\n", round, ret_outer, ret_inner);
+    ret++;
+  }
+  if (memcmp(outer, inner, bufsize)) {
+    printf("Round %d strings differ:\n - outer: %s\n - inner: %s\n", round, outer, inner);
+    ret++;
+  }
+  if (ret == 0)
+    printf("Round %d success: %s\n", round, outer);
+  return ret;
+}
+
+int main() {
+/* sizes of intrinsic types as reported by echo | cpp -dM | grep
+   SIZEOF, pruned to avoid floating point types.  Should work with
+   both clang and gcc, not sure about other C preprocessors.
+
+   Note that we set bits in every high octet and every low octet to
+   see that they end up in the right spot.
+ */
+  char c =             0x03L;
+  short s =           (0x04L << ((__SIZEOF_SHORT__ - 1) * 8))     + 0xff;
+  wchar_t wc =        (0x05L << ((__SIZEOF_WCHAR_T__ - 1) * 8))   + 0xfe;
+  int i =             (0x06L << ((__SIZEOF_INT__  - 1) * 8))      + 0xfd;
+  wint_t wi =         (0x07L << ((__SIZEOF_WINT_T__ - 1) * 8))    + 0xfc;
+  long l =            (0x08L << ((__SIZEOF_LONG__ - 1) * 8) )     + 0xfb;
+  long long ll =      (0x09LL << ((__SIZEOF_LONG_LONG__ - 1) * 8)) + 0xfa;
+  void *ptr = (void*)((0x0aL << ((__SIZEOF_POINTER__ - 1) * 8))   + 0xf9);
+  ptrdiff_t pd =      (0x0bL << ((__SIZEOF_PTRDIFF_T__ -1) * 8))  + 0xf9;
+  size_t sz =         (0x0cL << ((__SIZEOF_SIZE_T__ - 1) * 8))    + 0xf8;
+
+  char *buf[2];
+  for (int j = 0; j < 2; j++)
+    buf[j] = malloc(bufsize);
+
+  int ret[2];
+  int errors = 0;
+
+#define reset_buffers(n) for (int j = 0; j < 2; j++) memset(buf[j], n, bufsize)
+#define check_buffers(n) errors += compare_buffers(n, ret[0], ret[1], buf[0], buf[1])
+
+  reset_buffers(0);
+  ret[0] = outer(0, buf[0], c, s, wc, i, wi);
+  ret[1] = inner0(buf[1], c, s, wc, i, wi);
+  check_buffers(0);
+
+  reset_buffers(1);
+  ret[0] = outer(1, buf[0], l, ll, ptr, pd, sz);
+  ret[1] = inner1(buf[1], l, ll, ptr, pd, sz);
+  check_buffers(1);
+
+  return (int)errors;
+}

test/variadic/outer.c

@@ -0,0 +1,21 @@
+#include <stdarg.h>
+#include <time.h>
+#include "../../src/faketime_common.h"
+
+extern long inner0(char *out, ...);
+extern long inner1(char *out, ...);
+
+long outer(long num, char *out, ...) {
+  va_list ap;
+  va_start(ap, out);
+  variadic_promotion_t a[syscall_max_args];
+  for (int i = 0; i < syscall_max_args; i++)
+    a[i] = va_arg(ap, variadic_promotion_t);
+  va_end(ap);
+
+  if (num == 0)
+    return inner0(out, a[0], a[1], a[2], a[3], a[4], a[5]);
+  if (num == 1)
+    return inner1(out, a[0], a[1], a[2], a[3], a[4], a[5]);
+  else return -1;
+}