Add dlsym for oldfunc. (#8)

viferga · web-flow · commit 5b8cb6afc734 · 2025-04-15T11:13:13.000-04:00
diff --git a/Dockerfile b/Dockerfile
@@ -1,5 +1,6 @@
 # Dockerfile for QEMU testing
 # docker build -t metacall/plthook .
+
 FROM ubuntu:latest
 
 RUN apt update \
diff --git a/plthook_elf.c b/plthook_elf.c
@@ -899,7 +899,8 @@ int plthook_replace(plthook_t *plthook, const char *funcname, void *funcaddr, vo
                     }
                 }
                 if (oldfunc) {
-                    *oldfunc = *addr;
+                    void *prev = dlsym(RTLD_DEFAULT, funcname);
+                    *oldfunc = (prev != NULL) ? prev : *addr;
                 }
                 *addr = funcaddr;
                 if (!(prot & PROT_WRITE)) {

Original file line number	Diff line number	Diff line change
`@@ -899,7 +899,8 @@ int plthook_replace(plthook_t plthook, const char funcname, void *funcaddr, vo`
`899`	`899`	`}`
`900`	`900`	`}`
`901`	`901`	`if (oldfunc) {`
`902`		`- oldfunc = addr;`
	`902`	`+ void *prev = dlsym(RTLD_DEFAULT, funcname);`
	`903`	`+ oldfunc = (prev != NULL) ? prev : addr;`
`903`	`904`	`}`
`904`	`905`	`*addr = funcaddr;`
`905`	`906`	`if (!(prot & PROT_WRITE)) {`