From 2b0af8e76a81935f0a7e23bd6c61ca56761fb014 Mon Sep 17 00:00:00 2001
From: Jan Janssen <medhefgo@web.de>
Date: Fri, 10 Jun 2022 15:20:01 +0200
Subject: [PATCH 1/2] boot: Mark memcmp/memcpy/memset aliases as used

The compiler may emit calls to these but also optimize the function away
somehow, breaking at link stage. Marking them as used prevents this.
---
 src/boot/efi/efi-string.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/boot/efi/efi-string.c b/src/boot/efi/efi-string.c
index b9ef1548ca..f5b671c7be 100644
--- a/src/boot/efi/efi-string.c
+++ b/src/boot/efi/efi-string.c
@@ -294,9 +294,11 @@ void *efi_memset(void *p, int c, size_t n) {
 #  undef memcmp
 #  undef memcpy
 #  undef memset
-/* Provide the actual implementation for the builtins. To prevent a linker error, we mark memcpy/memset as
- * weak, because gnu-efi is currently providing them. */
-__attribute__((alias("efi_memcmp"))) int memcmp(const void *p1, const void *p2, size_t n);
-__attribute__((weak, alias("efi_memcpy"))) void *memcpy(void * restrict dest, const void * restrict src, size_t n);
-__attribute__((weak, alias("efi_memset"))) void *memset(void *p, int c, size_t n);
+/* Provide the actual implementation for the builtins by providing aliases. These need to be marked as used,
+ * as otherwise the compiler might remove them but still emit calls, which would break when linking.
+ * To prevent a different linker error, we mark memcpy/memset as weak, because gnu-efi is currently
+ * providing them. */
+__attribute__((used, alias("efi_memcmp"))) int memcmp(const void *p1, const void *p2, size_t n);
+__attribute__((used, weak, alias("efi_memcpy"))) void *memcpy(void * restrict dest, const void * restrict src, size_t n);
+__attribute__((used, weak, alias("efi_memset"))) void *memset(void *p, int c, size_t n);
 #endif

From 8494bd1ced5bed6f1960abda0e4c01df9dc56fd0 Mon Sep 17 00:00:00 2001
From: Jan Janssen <medhefgo@web.de>
Date: Fri, 10 Jun 2022 15:29:39 +0200
Subject: [PATCH 2/2] boot: Use memcpy/memset provided by firmware

These are significantly faster and safe us from rolling our own
optimized versions.
---
 src/boot/efi/efi-string.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/boot/efi/efi-string.c b/src/boot/efi/efi-string.c
index f5b671c7be..b8c576b8f0 100644
--- a/src/boot/efi/efi-string.c
+++ b/src/boot/efi/efi-string.c
@@ -263,6 +263,16 @@ void *efi_memcpy(void * restrict dest, const void * restrict src, size_t n) {
         if (!dest || !src || n == 0)
                 return dest;
 
+#ifdef SD_BOOT
+        /* The firmware-provided memcpy is likely optimized, so use that. The function is guaranteed to be
+         * available by the UEFI spec. We still make it depend on the boot services pointer being set just in
+         * case the compiler emits a call before it is available. */
+        if (_likely_(BS)) {
+                BS->CopyMem(dest, (void *) src, n);
+                return dest;
+        }
+#endif
+
         uint8_t *d = dest;
         const uint8_t *s = src;
 
@@ -280,6 +290,14 @@ void *efi_memset(void *p, int c, size_t n) {
         if (!p || n == 0)
                 return p;
 
+#ifdef SD_BOOT
+        /* See comment in efi_memcpy. Note that the signature has c and n swapped! */
+        if (_likely_(BS)) {
+                BS->SetMem(p, n, c);
+                return p;
+        }
+#endif
+
         uint8_t *q = p;
         while (n > 0) {
                 *q = c;