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doc: printf() codes
Document the format specifier codes used by U-Boot's printf() implementation. Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
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Heinrich Schuchardt
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@ -21,6 +21,7 @@ Implementation
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logging
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makefiles
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menus
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printf
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uefi/index
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version
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199
doc/develop/printf.rst
Normal file
199
doc/develop/printf.rst
Normal file
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@ -0,0 +1,199 @@
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.. SPDX-License-Identifier: GPL-2.0+
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Printf() format codes
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=====================
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Each conversion specification consists of:
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* leading '%' character
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* zero or more flags
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* an optional minimum field width
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* an optional precision field preceded by '.'
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* an optional length modifier
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* a conversion specifier
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Flags
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-----
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'space'
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fill up with spaces to reach the specified length
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\-
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left justify
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\+
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add sign field of decimal conversion
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#
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convert to alternative form
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* prepend 0 to octal output
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* ignored for decimal output
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* prepend 0X to hexadecimal output
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0
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fill up with zeroes to reach the specified length
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Integer types
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-------------
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Length modifiers
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''''''''''''''''
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The optional length modifier specifies the size of the argument.
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no modifier
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bool, enum, short, int are passed as int
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%h
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convert to (unsigned) short before printing.
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Only the low 16 bits are printed.
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%hh
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**not implemented**
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%j
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**not implemented**
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%l
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long
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%ll, %L
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long long
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%t
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ptr_diff_t
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%z, %Z
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size_t, ssize_t
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Conversion specifiers
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'''''''''''''''''''''
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Conversion specifiers control the output.
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%d
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signed decimal
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%u
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unsigned decimal
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%o
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unsigned octal
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%x
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unsigned lower case hexadecimal
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%X
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unsigned upper case hexadecimal
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The floating point conversion specifiers are not implemented:
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* %a
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* %A
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* %e
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* %E
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* %f
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* %F
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* %g
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* %G
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The following tables shows the correct combinations of modifiers and specifiers
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for the individual integer types.
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=================== ==================
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Type Format specifier
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=================== ==================
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bool %d, %x
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char %d, %x
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unsigned char %u, %x
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short %d, %x
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unsigned short %u, %x
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int %d, %x
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unsigned int %d, %x
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long %ld, %lx
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unsigned long %lu, %lx
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long long %lld, %llx
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unsigned long long %llu, %llx
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off_t %llu, %llx
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ptr_diff_t %td, %tx
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fdt_addr_t %pa, see pointers
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fdt_size_t %pa, see pointers
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phys_addr_t %pa, see pointers
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phys_size_t %pa, see pointers
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resource_size_t %pa, see pointers
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size_t %zu, %zx, %zX
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ssize_t %zd, %zx, %zX
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=================== ==================
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Characters
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----------
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%%
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a '%' character is written
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%c
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prints a single character
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%lc
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**not implemented**
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Strings
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-------
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%s
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prints a UTF-8 string (char \*)
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%ls
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prints a UTF-16 string (u16 \*)
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Pointers
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--------
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%p
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prints the address the pointer points to hexadecimally
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%pa, %pap
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prints the value of a phys_addr_t value that the pointer points to
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preceded with 0x and zero padding according to the size of phys_addr_t.
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The following types should be printed this way:
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* fdt_addr_t
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* fdt_size_t
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* phys_addr_t
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* phys_size_t
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* resource_size_t
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%pD
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prints a UEFI device path
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%pi4, %pI4
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prints IPv4 address, e.g. '192.168.0.1'
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%pm
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prints MAC address without separators, e.g. '001122334455'
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%pM
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print MAC address colon separated, e.g. '00:01:02:03:04:05'
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%pUb
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prints GUID big endian, lower case
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e.g. '00112233-4455-6677-8899-aabbccddeeff'
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%pUB
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prints GUID big endian, upper case
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e.g. '00112233-4455-6677-8899-AABBCCDDEEFF'
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%pUl
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prints GUID little endian, lower case
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e.g. '33221100-5544-7766-8899-aabbccddeeff'
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%pUL
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prints GUID little endian, upper case
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e.g. '33221100-5544-7766-8899-AABBCCDDEEFF'
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%pUs
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prints text description of a GUID or if such is not known little endian,
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lower case, e.g. 'system' for a GUID identifying an EFI system
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partition.
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