From b01995d16797396d75d6409c1937958ba7fe1c10 Mon Sep 17 00:00:00 2001
From: Leah Rowe <leah@libreboot.org>
Date: Sun, 26 Jan 2025 08:47:01 +0000
Subject: [PATCH] util/nvmutil: make cmd_swap its own function again

previous audits sizecoded nvmutil.c, reducing the sloccount,
but this resulted in unreadable code.

move the swap logic (swap parts) back to its own function,
for clarity.

Signed-off-by: Leah Rowe <leah@libreboot.org>
---
 util/nvmutil/nvmutil.c | 40 ++++++++++++++++++++++++++--------------
 1 file changed, 26 insertions(+), 14 deletions(-)

diff --git a/util/nvmutil/nvmutil.c b/util/nvmutil/nvmutil.c
index 5b54117..be02961 100644
--- a/util/nvmutil/nvmutil.c
+++ b/util/nvmutil/nvmutil.c
@@ -17,7 +17,8 @@
 void cmd_setchecksum(void), cmd_brick(void), swap(int partnum), writeGbe(void),
     cmd_dump(void), cmd_setmac(void), readGbe(void), checkdir(const char *path),
     macf(int partnum), hexdump(int partnum), openFiles(const char *path),
-    cmd_copy(void), parseMacString(const char *strMac, uint16_t *mac);
+    cmd_copy(void), parseMacString(const char *strMac, uint16_t *mac),
+    cmd_swap(void);
 int goodChecksum(int partnum);
 uint8_t hextonum(char chs), rhex(void);
 
@@ -46,7 +47,7 @@ typedef struct op {
 op_t op[] = {
 { .str = "dump", .cmd = cmd_dump, .args = 3},
 { .str = "setmac", .cmd = cmd_setmac, .args = 3},
-{ .str = "swap", .cmd = writeGbe, .args = 3},
+{ .str = "swap", .cmd = cmd_swap, .args = 3},
 { .str = "copy", .cmd = cmd_copy, .args = 4},
 { .str = "brick", .cmd = cmd_brick, .args = 4},
 { .str = "setchecksum", .cmd = cmd_setchecksum, .args = 4},
@@ -148,8 +149,8 @@ main(int argc, char *argv[])
 	readGbe(); /* read gbe file into memory */
 	(*cmd)(); /* operate on gbe file in memory, as per user command */
 
-	if ((gbeFileChanged) && (flags != O_RDONLY) && (cmd != writeGbe))
-		writeGbe(); /* not called for swap cmd; swap calls writeGbe */
+	if ((gbeFileChanged) && (flags != O_RDONLY))
+		writeGbe();
 
 	err_if((errno != 0) && (cmd != cmd_dump)); /* don't err on dump */
 	return errno; /* errno can be set by the dump command */
@@ -197,7 +198,7 @@ openFiles(const char *path)
 void
 readGbe(void)
 {
-	if ((cmd == writeGbe) || (cmd == cmd_copy))
+	if ((cmd == cmd_swap) || (cmd == cmd_copy))
 		nf = partsize; /* read/write the entire block */
 	else
 		nf = 128; /* only read/write the nvm part of the block */
@@ -378,6 +379,20 @@ cmd_copy(void)
 	/* we simply set the right nvm part as changed, and write the file */
 }
 
+/* swap contents between the two parts */
+void
+cmd_swap(void) {
+	err_if(!(goodChecksum(0) || goodChecksum(1)));
+	errno = 0;
+
+	/* speedhack: swap pointers, not words. (xor swap) */
+	gbe[0] ^= gbe[1];
+	gbe[1] ^= gbe[0];
+	gbe[0] ^= gbe[1];
+
+	gbeFileChanged = nvmPartChanged[0] = nvmPartChanged[1] = 1;
+}
+
 /* verify nvm part checksum (return 1 if valid) */
 int
 goodChecksum(int partnum)
@@ -398,16 +413,13 @@ goodChecksum(int partnum)
 void
 writeGbe(void)
 {
-	if (cmd == writeGbe) /* cmd swap calls writeGbE; need valid checksum */
-		err_if(!(goodChecksum(0) || goodChecksum(1)));
-
-	for (int p = 0, x = (cmd == writeGbe) ? 1 : 0; p < 2; p++) {
-		if ((!nvmPartChanged[p]) && (cmd != writeGbe))
+	for (int p = 0; p < 2; p++) {
+		if ((!nvmPartChanged[p]))
 			continue;
 
-		swap(p ^ x); /* swap bytes on big-endian host CPUs */
+		swap(p); /* swap bytes on big-endian host CPUs */
 
-		err_if(pwrite(fd, (uint8_t *) gbe[p ^ x], nf, p * partsize)
+		err_if(pwrite(fd, (uint8_t *) gbe[p], nf, p * partsize)
 		    == -1);
 	}
 
@@ -417,8 +429,8 @@ writeGbe(void)
 
 /* swap byte order on big-endian CPUs. swap skipped on little endian */
 void
-swap(int partnum)
-{
+swap(int partnum) /* swaps bytes in words, not pointers. */
+{		/* not to be confused with cmd_swap */
 	size_t w, x;
 	uint8_t *n = (uint8_t *) gbe[partnum];