notes: objdump (osx)

notes/2018_011_objdump/.gitignore

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+test
+*.o

notes/2018_011_objdump/Makefile

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+.PHONY: clean
+
+LIBS = -lmikey
+CFLAGS = -Wall -Wextra -pedantic -std=c99
+OBJECTS = addone.o
+
+all: test
+
+test: test.c $(OBJECTS)
+	$(CC) -o $@ $^ $(CFLAGS) $(LIBS)
+
+clean:
+	rm -f test
+	rm -f *.o

notes/2018_011_objdump/addone.c

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+#include <stdio.h>
+#include <mikey/common.h>
+
+int addone(int x) {
+    return x + 1;
+}

notes/2018_011_objdump/addone.h

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+#ifndef _ADDONE_H
+#define _ADDONE_H
+
+int addone(int x);
+
+#endif

notes/2018_011_objdump/notes.org

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+
+* notes
+
+I am running this on OSX; this is the llvm =objdump= which is
+quite different from the linux utility (I believe).
+
+* print the symbol table
+
+For instance, on the =test= executable:
+
+#+BEGIN_SRC sh :results verbatim
+objdump -t test
+#+END_SRC
+
+#+RESULTS:
+#+begin_example
+
+test:	file format Mach-O 64-bit x86-64
+
+SYMBOL TABLE:
+0000000100001018 l       __DATA,__data	_TESTING
+0000000100000000 g     F __TEXT,__text	__mh_execute_header
+0000000100000f40 g     F __TEXT,__text	_addone
+0000000100000ee0 g     F __TEXT,__text	_main
+0000000000000000         *UND*	_printf
+0000000000000000         *UND*	dyld_stub_binder
+#+end_example
+
+here there is a reference to the static text in the data segment,
+=TESTING=, the functions in the text segment, =addone= and
+=main=. Note that =addone= comes from the =addone.o= object file:
+
+#+begin_src sh :results verbatim
+objdump -t addone.o
+#+end_src
+
+#+RESULTS:
+: 
+: addone.o:	file format Mach-O 64-bit x86-64
+: 
+: SYMBOL TABLE:
+: 0000000000000000 g     F __TEXT,__text	_addone
+
+There are also references to the dynamically linked =printf=. I think
+(but not sure) =*UND*= means undefined, as the dynamic linker will
+determine at runtime the location of this function.
+
+* disassembling
+
+we can disassemble a particular symbol, for instance:
+
+#+begin_src sh :results verbatim
+objdump -D -macho -dis-symname=_addone addone.o
+#+end_src
+
+#+RESULTS:
+#+begin_example
+addone.o:
+(__TEXT,__text) section
+_addone:
+       0:	55 	pushq	%rbp
+       1:	48 89 e5 	movq	%rsp, %rbp
+       4:	89 7d fc 	movl	%edi, -4(%rbp)
+       7:	8b 7d fc 	movl	-4(%rbp), %edi
+       a:	83 c7 01 	addl	$1, %edi
+       d:	89 f8 	movl	%edi, %eax
+       f:	5d 	popq	%rbp
+      10:	c3 	retq
+#+end_example

notes/2018_011_objdump/test.c

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+#include <stdio.h>
+#include <mikey/common.h>
+#include "addone.h"
+
+static char* TESTING = "This is a static string.\n";
+
+int main()
+{
+    printf("Foo.\n");
+    printf("%s", TESTING);
+    printf("One plus two is: %d", addone(2));
+    return EXIT_SUCCESS;
+}