From 33659d246e5d89885413d4ea30525dacdacc56ee Mon Sep 17 00:00:00 2001 From: Maximilian Brune Date: Wed, 24 Jan 2024 07:40:14 +0100 Subject: arch/arm64/armv8: Add exception output without printk In case printk does not work the current exception handler will print a simple "!" to notify the developer that coreboot is actually there but something went wrong. The "!" can be quite confusing when it actually happens that printk does not work. Since "!" doesn't really say much (if you don't know the exception arm64 code) the developer (like me) can easily assume that something went wrong while configuring clocks or baud rate of UART, since the output seemingly does not seem to make sense. This adds a little bit more output to assure the developer that what was printed was actually intended to be printed. Therefore it prints "EXCEPT" which assures the developer that this was intended output. It also adds a comment above so that developer can more easily grep for this message. It has intentionally not been written as: ``` const char *msg = "\r\n!EXCPT!"; while (*msg) __uart_tx_byte(*msg++); ``` because in this case the compiler will generate code that will place `msg` somewhere in bootblock and the code will try to access this using a memory address. In rare cases (if you link bootblock at the wrong address) this memory address can be wrong and coreboot will not print the message. Using individual calls to `__uart_tx_byte` ensures that the compiler will generate code which directly puts the character bytes into the argument register without referencing a variable in bootblock. Signed-off-by: Maximilian Brune Change-Id: I2f858730469fff3cae120fd7c32fec53b3d309ca Reviewed-on: https://review.coreboot.org/c/coreboot/+/80184 Reviewed-by: Julius Werner Tested-by: build bot (Jenkins) --- src/arch/arm64/armv8/exception.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'src/arch') diff --git a/src/arch/arm64/armv8/exception.c b/src/arch/arm64/armv8/exception.c index 15d7e38398ad..8583fd51722e 100644 --- a/src/arch/arm64/armv8/exception.c +++ b/src/arch/arm64/armv8/exception.c @@ -101,10 +101,21 @@ enum cb_err exception_handler_unregister(uint64_t vid, struct exception_handler static void print_exception_info(struct exc_state *state, uint64_t idx) { - /* Poor man's sign of life in case printk() is shot. */ + /* + * Sign of life in case printk() is shot. Prints !EXCEPT! to UART + * Not using a loop but instead calling __uart_tx_byte separately is intentionally here + * because in rare cases it will not print if it needs to access memory addresses + */ __uart_tx_byte('\r'); __uart_tx_byte('\n'); __uart_tx_byte('!'); + __uart_tx_byte('E'); + __uart_tx_byte('X'); + __uart_tx_byte('C'); + __uart_tx_byte('E'); + __uart_tx_byte('P'); + __uart_tx_byte('T'); + __uart_tx_byte('!'); printk(BIOS_DEBUG, "\nexception %s\n", idx < NUM_EXC_VIDS ? exception_names[idx] : "_unknown"); -- cgit v1.2.3