Sanity Checks¶
If you run with the –check argument, memtab will perform a few “sanity checks” against some other tools that produce similar measures of memory resource utilization.
Comparing Against size Output¶
The size tool, from GNU’s binutils, provides the highest level assessment of the memory usage of an ELF file. It provides a breakdown of the memory usage by section, and also provides a total for the entire ELF file. The output of size is in the following format:
text data bss dec hex filename 1234 5678 9101 12345 0x3039 my.elf
Memtab will run size, capture the output, and then compare the numbers from size against the numbers from readelf described in the next section.
Comparing Against readelf Output¶
Readelf can output details at a few levels. One level is the “section”, which should be on the dozens-of-lines territory. You can also output at the symbol level, which will be hundreds or thousands of lines, similar to nm.
The output of readelf is in the following format:
Section Headers: [Nr] Name Type Addr Off Size ES Flg Lk Inf Al [ 0] NULL 00000000 000000 000000 00 0 0 0 [ 1] .interp PROGBITS 00000000 000040 00001c 00 A 0 0 1 [ 2] .note.gnu.build-id NOTE 00000000 00005c 000024 00 A 0 0 16 [ 3] .gnu.hash GNU_HASH 00000000 000080 000030 04 A 10 0 16 [ … ]
- And then symbols are listed in the following format:
- Symbol table ‘.symtab’ contains 1234 entries:
- Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND 1: 0000000000000000 0 SECTION LOCAL DEFAULT 1 2: 0000000000000000 0 SECTION LOCAL DEFAULT 2 … 1233: 0000000000401000 4 OBJECT GLOBAL DEFAULT 10 _start
Memtab will run readelf, capture the output, and the compare the numbers from readelf against the numbers from size described in the previous section. It also uses readelf though to get the total sizes for each region, as well as the addresses covered, so it can allocate symbols to those regions.
Comparing Against objdump Output¶
Objdump is similar to readelf, and as such is currently used the least. We just run objdump, capture the output to local memory, and compare against the other tools like size just to make sure the numbers make sense together. It is currently not used to inform the overall output of memtab at all.
Comparing Against the ld –print-memory-usage Output¶
The ld linker has a –print-memory-usage option that prints out the memory usage of the different regions defined in the linker script. More documentation on that can be found here.
Unfortunately, this requires the link operation to actually occur - as in, the inputs are the linker script and all of the .o files that are being linked together to produce the .elf. At the time of this writing, I could not determine a way to produce this output given just the elf, or even the elf + a linker script.
Therefore, to perform this sanity check, we will have to copy off the output of the –print-memory-usage to a separate file, and then compare the memtab results against the data in that file. Its not perfect, but its better than nothing.
Note - to get this in zephyr, you need to define OUTPUT_PRINT_MEMORY_USAGE in your KConfig settings.