[PATCH lttng-ust] Add trace support for calloc and realloc.

[Stefan Seefeld <stefan_seefeld@mentor.com>]

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The attached patch adds support for calloc and realloc to the
lttng-ust-libc-wrapper library.

The implementation for calloc is slightly tricky, as dlsym calls calloc
internally, so the library needs to provide a 'dummy' implementation for
calloc to avoid an endless recursion. Testing has shown however that the
object(s) allocated at that point are small, so a dummy static 'heap'
suffices as a workaround.

-- 
Stefan Seefeld
CodeSourcery / Mentor Graphics
http://www.mentor.com/embedded-software/


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From 78696689a46c13cdd2625c59348cbb1c03a32b0e Mon Sep 17 00:00:00 2001
From: Stefan Seefeld <stefan_seefeld@mentor.com>
Date: Sat, 27 Jul 2013 01:10:23 -0400
Subject: [PATCH] Add trace support for calloc and realloc.

Signed-off-by: Stefan Seefeld <stefan_seefeld@mentor.com>
---
 liblttng-ust-libc-wrapper/lttng-ust-malloc.c | 68 ++++++++++++++++++++++++++++
 liblttng-ust-libc-wrapper/ust_libc.h         | 18 ++++++++
 2 files changed, 86 insertions(+)

diff --git a/liblttng-ust-libc-wrapper/lttng-ust-malloc.c b/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
index 3212ff0..772663a 100644
--- a/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
+++ b/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
@@ -57,3 +57,71 @@ void free(void *ptr)
 	tracepoint(ust_libc, free, ptr);
 	plibc_free(ptr);
 }
+
+/*
+   The following 'dummy' variables and functions are needed
+   to break out of an endless recursion:
+   dlsym itself appears to call calloc, so we need to provide
+   an implementation for the very first call to calloc to use.
+*/
+
+#define DUMMY_HEAP_SIZE 1024
+static char dummy_heap[DUMMY_HEAP_SIZE] = {0};
+static int dummy_end_of_heap = 0;
+
+static void *dummy_malloc(size_t size)
+{
+    if(size == 0)
+	return NULL;
+
+    size_t dummy_end_of_heap_reserved = dummy_end_of_heap + size;
+    if(dummy_end_of_heap_reserved >= DUMMY_HEAP_SIZE)
+	return NULL;
+
+    void *loc = (void*) &dummy_heap[dummy_end_of_heap];
+    dummy_end_of_heap = dummy_end_of_heap_reserved;
+    return loc;
+};
+
+static void *dummy_calloc(size_t nmemb, size_t size)
+{
+  return dummy_malloc(nmemb * size);
+}
+
+void *calloc(size_t nmemb, size_t size)
+{
+        static void *(* volatile plibc_calloc)(size_t nmemb, size_t size) = NULL;
+	void *retval;
+
+	if (plibc_calloc == NULL) {
+	        /* Temporarily redirect to dummy_calloc,
+		   until the dlsym lookup has completed. */
+                plibc_calloc = dummy_calloc;
+		plibc_calloc = dlsym(RTLD_NEXT, "calloc");
+		if (plibc_calloc == NULL) {
+			fprintf(stderr, "callocwrap: unable to find calloc\n");
+			return NULL;
+		}
+	}
+	retval = plibc_calloc(nmemb, size);
+	tracepoint(ust_libc, calloc, nmemb, size, retval);
+	return retval;
+}
+
+void *realloc(void *ptr, size_t size)
+{
+        static void *(*plibc_realloc)(void *ptr, size_t size) = NULL;
+	void *retval;
+
+	if (plibc_realloc == NULL) {
+		plibc_realloc = dlsym(RTLD_NEXT, "realloc");
+		if (plibc_realloc == NULL) {
+			fprintf(stderr, "reallocwrap: unable to find realloc\n");
+			return NULL;
+		}
+	}
+	retval = plibc_realloc(ptr, size);
+	tracepoint(ust_libc, realloc, ptr, size, retval);
+	return retval;
+}
+
diff --git a/liblttng-ust-libc-wrapper/ust_libc.h b/liblttng-ust-libc-wrapper/ust_libc.h
index af705aa..6b03a4d 100644
--- a/liblttng-ust-libc-wrapper/ust_libc.h
+++ b/liblttng-ust-libc-wrapper/ust_libc.h
@@ -47,6 +47,24 @@ TRACEPOINT_EVENT(ust_libc, free,
 	)
 )
 
+TRACEPOINT_EVENT(ust_libc, calloc,
+	TP_ARGS(size_t, nmemb, size_t, size, void *, ptr),
+	TP_FIELDS(
+		ctf_integer(size_t, nmemb, nmemb)
+		ctf_integer(size_t, size, size)
+		ctf_integer_hex(unsigned long, ptr, (unsigned long) ptr)
+	)
+)
+
+TRACEPOINT_EVENT(ust_libc, realloc,
+	TP_ARGS(void *, in_ptr, size_t, size, void *, ptr),
+	TP_FIELDS(
+		ctf_integer_hex(unsigned long, in_ptr, (unsigned long) in_ptr)
+		ctf_integer(size_t, size, size)
+		ctf_integer_hex(unsigned long, ptr, (unsigned long) ptr)
+	)
+)
+
 #endif /* _TRACEPOINT_UST_LIBC_H */
 
 #undef TRACEPOINT_INCLUDE
-- 
1.8.3.1


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