".byte 0x3f" instructions in disassembly

Graggi
Posts: 7
Joined: Thu Jun 29, 2023 7:49 pm

".byte 0x3f" instructions in disassembly

Postby Graggi » Thu Jul 06, 2023 9:46 pm

Hi,

I'm using xtensa-esp32-elf-objdump[1] to analysis some ESP32-Binaries. I noticed that sometimes 0x3f single byte instructions(?) can be found in the disassembly.

For example:
3f.png
3f.png (69.07 KiB) Viewed 31139 times
I could not find any mentioning of this in the Xtensa-ISA[2]. Why are they placed there?

Regards

[1] https://github.com/badgeteam/xtensa-esp ... master/bin
[2] https://esp32.com/download/file.php?id=10134

ESP_Sprite
Posts: 9708
Joined: Thu Nov 26, 2015 4:08 am

Re: ".byte 0x3f" instructions in disassembly

Postby ESP_Sprite » Fri Jul 07, 2023 8:52 am

Objdump is not very smart and may be trying to decode non-instruction areas, like literal pools.

ESP_igrr
Posts: 2071
Joined: Tue Dec 01, 2015 8:37 am

Re: ".byte 0x3f" instructions in disassembly

Postby ESP_igrr » Fri Jul 07, 2023 7:03 pm

This could also be caused by the ELF file missing additional xtensa-specific sections; we have fixed this issue in https://github.com/espressif/esp-idf/co ... 98277fb3bb, but it could be that your ELF file was built with an IDF version which doesn't contain that fix.

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