[avr-libc-dev] [bug #49567] Use meta-info from --print-multi-lib and --print-multi-directory

[Georg-Johann Lay]

URL:
  <http://savannah.nongnu.org/bugs/?49567>

                 Summary: Use meta-info from --print-multi-lib and
--print-multi-directory
                 Project: AVR C Runtime Library
            Submitted by: gjlayde
            Submitted on: Wed 09 Nov 2016 02:32:38 PM GMT
                Category: Build Infrastructure
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Build system
                  Status: None
        Percent Complete: 0%
             Assigned to: None
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 2.0.0
           Fixed Release: None

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Details:

Currently, all the multilib layout and device -> multilib mapping and multilib
-> options mapping is hand coded in scripts like devtools/gen-avr-lib-tree.sh

avr-gcc is able to provide information about the multilib layout.  Using this
feature can be used to dynamically adjust avr-libc build machinery to the
actual multilib layout implemented by avr-gcc.

* Left of ";" you see the relative path where the files belonging to
respective multilib variant will be situated.

* Right of ";" are the options ("@" stands for " -") to select that multilib)


$ avr-gcc --print-multi-lib

.;
avr25;@mmcu=avr25
avr3;@mmcu=avr3
avr31;@mmcu=avr31
avr35;@mmcu=avr35
avr4;@mmcu=avr4
avr5;@mmcu=avr5
avr51;@mmcu=avr51
avr6;@mmcu=avr6
avrxmega2;@mmcu=avrxmega2
avrxmega4;@mmcu=avrxmega4
avrxmega5;@mmcu=avrxmega5
avrxmega6;@mmcu=avrxmega6
avrxmega7;@mmcu=avrxmega7
avrtiny;@mmcu=avrtiny
tiny-stack;@msp8
avr25/tiny-stack;@address@hidden


Notice how -msp8 is required to select "tiny-stack" (and *not* -mtiny-stack)
which cause quite some confusion in the past.

In order to find out in which multilib a specific device is located, there is


$ avr-gcc -mmcu=at43usb320 --print-multi-directory
avr31

$ avr-gcc -mmcu=attiny261 --print-multi-directory
avr25/tiny-stack


The advantage of factoring out multilib layout is obvious.  Suppose there is
some avr-gcc flaw like http://gcc.gnu.org/PR78275 aka.
https://savannah.nongnu.org/bugs/index.php?49565

If meta information from the compiler driver was used, there wouldn't have
been a need to file a libc bug for a wrong multilib for AT43usb320 because
avr-libc would factor out the multilib location and draw that information from
avr-gcc.





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