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Re: [Patch, avr] Place progmem.data from avr-libc above other progmem
- From: Alan Modra <amodra at gmail dot com>
- To: Senthil Kumar Selvaraj <senthil_kumar dot selvaraj at atmel dot com>
- Cc: Nick Clifton <nickc at redhat dot com>, binutils at sourceware dot org, Denis Chertykov <chertykov at gmail dot com>
- Date: Wed, 18 May 2016 17:45:47 +0930
- Subject: Re: [Patch, avr] Place progmem.data from avr-libc above other progmem
- Authentication-results: sourceware.org; auth=none
- References: <87oa8832kx dot fsf at atmel dot com> <fb734ee9-5592-716c-787d-4e9036863477 at redhat dot com> <87eg8z3j2l dot fsf at atmel dot com>
On Wed, May 18, 2016 at 01:15:54PM +0530, Senthil Kumar Selvaraj wrote:
> Nick Clifton writes:
> > Hi Senthil,
> >> avr-libc's vfprint handling uses a lookup table located in flash
> >> if float format specifiers are involved. If user code also has
> >> lots of flash data (in section .progmem.data), then
> >> avr-libc's progmem data gets pushed beyond the 64 K word limit. The
> >> avr-libc code doesn't expect this to happen and vfprintf stops working correctly.
> > Doesn't this indicate a problem with the linker - in that it does not
> > report to the user that the code is broken and that accesses above the 64k
> > limit are being made without use of the memx address space modifier ?
> Do you mean reloc processing should have detected the overflow? In
> this case, the offending value is loaded into two 8 bit regs, using the
> lo8 and hi8 modifiers, resulting in R_AVR_LO8_LDI_NEG and
> R_AVR_HI8_LDI_NEG relocs. I guess if there was a single reloc that
> handled the value, we could have detected overflow, AVR has only 8 bit
> registers though, so I can't see a way to do this. Am I missing something?
The problem of values being split over multiple insns is not one that
should affect AVR since you use RELA relocs. The value ought to be
available at each of the R_AVR_LO8_LDI_NEG and R_AVR_HI8_LDI_NEG
relocs as the symbol value plus reloc addend.
Australia Development Lab, IBM