internal: add a wrapper for __libc_start_main for PowerPC(64(le))

This is necessary because the musl and glibc function signatures
differ significantly.

1 files changed, 41 insertions, 0 deletions

diff --git a/libgcompat/internal.c b/libgcompat/internal.c
index 450c5e4..53ac429 100644
--- a/libgcompat/internal.c
+++ b/libgcompat/internal.c
@@ -2,6 +2,47 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#if defined(__powerpc__)
+
+/* On PowerPC as well as ppc64, we need to fix up __libc_start_main as the
+ * glibc and musl versions have wildly different signatures, which would
+ * result in the arguments to __libc_start_main being completely wrong.
+ *
+ * Using dlsym in this context is mildly questionable as this is before
+ * the full initialization has been done, but there is no better way.
+ */
+
+#include <dlfcn.h>
+
+struct startup_info {
+	void *sda_base;
+	void *f_main;
+	void *f_init;
+	void *f_fini;
+};
+
+typedef int (*start_main_t)(void *mf, int argc, char **argv);
+
+/*
+ * ref: https://git.musl-libc.org/cgit/musl/tree/crt/crt1.c?id=90251cf
+ * ref: https://git.musl-libc.org/cgit/musl/tree/src/env/__libc_start_main.c?id=90251cf#n71
+ * ref: https://github.com/bminor/glibc/blob/5cb226d/sysdeps/unix/sysv/linux/powerpc/libc-start.c#L36
+ */
+int __libc_start_main(void *argc, void *argv, void *ev, void *auxv, void *fini,
+                      struct startup_info *si, long *p)
+{
+	(void)argc;
+	(void)argv;
+	(void)ev;
+	(void)auxv;
+	(void)fini;
+	/* argc/argv from the stack, main from startup_info */
+	start_main_t mainf = (start_main_t)dlsym(RTLD_NEXT, "__libc_start_main");
+	return mainf(si->f_main, *p, (void *)(p + 1));
+}
+
+#endif /* defined(__powerpc__) */
+
 void GCOMPAT__panic(const char *fmt, ...)
 {
 	va_list va;