misc: replace VLAs with alloca()

Replace all variable-length arrays with a call to `alloca()`. This doesn't solve the problem, and merely papers over it. However, there are two benefits to this approach: 1. We can now grep for `alloca()` in order to find all uses of VLAs 2. This helps to build under MSVC, which simply doesn't support VLAs Signed-off-by: Sean Cross <[email protected]>
blackmagic-debug · Nov 29, 2023 · 672dad7 · 672dad7
1 parent 2bda2af
commit 672dad7
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Showing 5 changed files with 15 additions and 10 deletions.
diff --git a/src/gdb_main.c b/src/gdb_main.c
@@ -143,7 +143,7 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 		ERROR_IF_NO_TARGET();
 		const size_t reg_size = target_regs_size(cur_target);
 		if (reg_size) {
-			uint8_t gp_regs[reg_size];
+			uint8_t *gp_regs = alloca(reg_size);
 			target_regs_read(cur_target, gp_regs);
 			gdb_putpacket(hexify(pbuf, gp_regs, reg_size), reg_size * 2U);
 		} else {
@@ -160,7 +160,7 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 			break;
 		}
 		DEBUG_GDB("m packet: addr = %" PRIx32 ", len = %" PRIx32 "\n", addr, len);
-		uint8_t mem[len];
+		uint8_t *mem = alloca(len);
 		if (target_mem_read(cur_target, mem, addr, len))
 			gdb_putpacketz("E01");
 		else
@@ -171,7 +171,7 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 		ERROR_IF_NO_TARGET();
 		const size_t reg_size = target_regs_size(cur_target);
 		if (reg_size) {
-			uint8_t gp_regs[reg_size];
+			uint8_t *gp_regs = alloca(reg_size);
 			unhexify(gp_regs, &pbuf[1], reg_size);
 			target_regs_write(cur_target, gp_regs);
 		}
@@ -189,7 +189,7 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 			break;
 		}
 		DEBUG_GDB("M packet: addr = %" PRIx32 ", len = %" PRIx32 "\n", addr, len);
-		uint8_t mem[len];
+		uint8_t *mem = alloca(len);
 		unhexify(mem, pbuf + hex, len);
 		if (target_mem_write(cur_target, addr, mem, len))
 			gdb_putpacketz("E01");
@@ -268,7 +268,7 @@ int gdb_main_loop(target_controller_s *tc, char *pbuf, size_t pbuf_size, size_t
 			int n;
 			sscanf(pbuf, "P%" SCNx32 "=%n", &reg, &n);
 			// TODO: FIXME, VLAs considered harmful.
-			uint8_t val[strlen(pbuf + n) / 2U];
+			uint8_t *val = alloca(strlen(pbuf + n) / 2U);
 			unhexify(val, pbuf + n, sizeof(val));
 			if (target_reg_write(cur_target, reg, val, sizeof(val)) > 0)
 				gdb_putpacketz("OK");
@@ -403,7 +403,7 @@ static void exec_q_rcmd(const char *packet, const size_t length)
 	else {
 		const char *const response = "Failed\n";
 		const size_t response_length = strlen(response);
-		char pbuf[response_length * 2 + 1];
+		char *pbuf = alloca(response_length * 2 + 1);
 		gdb_putpacket(hexify(pbuf, response, response_length), 2 * response_length);
 	}
 }

diff --git a/src/include/general.h b/src/include/general.h
@@ -33,6 +33,11 @@
 // NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
 #define __USE_MINGW_ANSI_STDIO 1
 #endif
+#if defined(_WIN32) || defined(__CYGWIN__)
+#include <malloc.h>
+#else
+#include <alloca.h>
+#endif
 #include <stdint.h>
 #include <stdbool.h>
 #include <stdlib.h>

diff --git a/src/rtt.c b/src/rtt.c
@@ -89,9 +89,9 @@ static uint32_t fast_search(target_s *const cur_target, const uint32_t ram_start
 	static const uint64_t r = 0x73b07d01;
 	static const uint32_t stride = 128;
 	uint64_t t = 0;
-	uint8_t srch_buf[m + stride];
+	uint8_t *srch_buf = alloca(m + stride);
 
-	memset(srch_buf, 0, sizeof(srch_buf));
+	memset(srch_buf, 0, m + stride);
 
 	for (uint32_t addr = ram_start; addr < ram_end; addr += stride) {
 		uint32_t buf_siz = MIN(stride, ram_end - addr);

diff --git a/src/target/adiv5.c b/src/target/adiv5.c
@@ -544,7 +544,7 @@ static void adiv5_component_probe(
 	}
 
 #if defined(ENABLE_DEBUG)
-	char indent[recursion + 1U];
+	char *indent = alloca(recursion + 1U);
 
 	for (size_t i = 0; i < recursion; i++)
 		indent[i] = ' ';

diff --git a/src/target/msp432p4.c b/src/target/msp432p4.c
@@ -285,7 +285,7 @@ static bool msp432_flash_write(target_flash_s *f, target_addr_t dest, const void
 	DEBUG_WARN("Flash protect: 0x%08" PRIX32 "\n", target_mem_read32(t, mf->flash_protect_register));
 
 	/* Prepare input data */
-	uint32_t regs[t->regs_size / sizeof(uint32_t)]; // Use of VLA
+	uint32_t *regs = alloca(t->regs_size / sizeof(uint32_t)); // Use of VLA
 	target_regs_read(t, regs);
 	regs[0] = SRAM_WRITE_BUFFER; // Address of buffer to be flashed in R0
 	regs[1] = dest;              // Flash address to be write to in R1